Spaces Between The Gaps: acrylic painting

Square Brush / Square Touch Brushwork Technique

Wednesday, September 28, 2011

Pickled Eggplant - Fiona Morgan. An example of square brush in my work.

There was once only one way for a painting to be. The surface had to be smooth, the brushstrokes invisible. Anything less was considered scandalously unfinished. This is talking about the history of European painting of course. Over time, this idea has loosened. Broad brushstrokes, suggestions of detail, obvious brushmarks are now obliviously normal.

Detail of Bastien Lepage's Sarah Bernhardt showing the loose brushwork that has influenced so many modern painters today.

The impressionists really smashed the idea of hiding every brushstroke, but the idea had been gaining ground for quite some time. The artists Velaquez, Bastien Lepage and even as far back as Rembrandt had been toying with letting the painterlyness of paint do the talking.

Angela Morgan painting featuring square brush technique

Angela Morgan (no, not a relative!) makes a real feature of square brush technique in her work.

Square brush or square touch technique is a version of the broken brushstroke technique the Impressionists were famous for, and it is common today.

Detail of a Joe Sorren painting showing off square brush technique in the background

Detail of a Joe Sorren painting showing off the square brush backgrounds I love in his work.

Usually using brights, flats or filberts, the flat of the paintbrush is used to lay down squarish strokes of paint directly, unblended, in a jigsaw pattern.

Aldro T Hibbard, and many of the Rockport school of painting are characterised by a square brush technique.

It gives a chunky feeling which is great for modelling structure. Different planes of an object can be deliniated easily with different temperature strokes and different values.

Arthur Streeton showcasing the atmospheric quality of square brush.

It easily gives soft edges useful for atmosphere and light.

Daily painter Layne Cook with a dramatic square touch example showing the removal of detail.

The size of the squares eliminates distracting detail and therefore has a unifying effect on the painting as a whole. Anything smaller than one square stroke has to be really important to be included. This eliminates visual clutter, focussing the viewer on the most important aspects of the painting.

Dean Cornwell showing the square touch painting technique

Dean Cornwell with an excellent example of fooling the eye into seeing more detail than is actually there. Look at the greys - the timbers and the ground.

It gives a pixellating vibrancy to the surface of the painting. Each stroke can be a slightly different colour and angle which makes the painting appear to sing with more colour and detail than is actually there. The eye detects colour changes and hints of detail. Square touch is a way of fooling the brain into adding what it thinks should be there. Thank you impressionistic heritage.

Sir Henry Raeburn, Scottish portrait painter, managed to subtley use square touch throughout his career of figurative painting, despite being ahead of his time and the difficulty of this technique in portraiture. It's much more suited to still life and landscape.

A most excellent wrap up of square brush technique is over on Stapletearn Kearn's blog. Muchly recommended.

http://stapletonkearns.blogspot.com/2010/07/more-on-brushstroke.html

There are loads of artists who make great use of this painterly technique. Know of an artist whose work is loaded with square brush? Tell us! Leave a comment.

Photographing Paintings For Artists Records

Thursday, January 27, 2011

Photo by Arty Smokes

So the paintings are finished and ready to go to new homes and you want to record your work for posterity. How to do this professionally at home without needing studio lights.

What you will need

Your dry artwork, unvarnished
A bright overcast day - yes outdoors in diffuse sunlight is actually the best solution to photographing shiny oil paintings if you don't have a studio setup
A camera, preferably digital (does anyone even use film cameras any more?) and even better, DSLR - check that the megapixel capability of your camera is sufficient for the size of print that you may want for your records. Here is a useful megapixel to print size chart
A good camera lens without any distortion or vignetting
A polarizing filter for your camera lens - this is to cut out glare from highlights
A tripod
A grey card - this will make your colour correcting a breeze (yes this is an affiliate link)
A sturdy support for your painting
A dark piece of cloth or paper - this is to minimise or prevent a colour cast from the surroundings

The photography setup

Wait until your painting dries.

You will get the best photos of dry or nearly dry oil paintings. If the oil is still wet, it will shine in areas and the oil remaining in the painting will reflect light differently than the dry areas of the painting.

Go outside on a bright overcast day.
This is crucial. I've tried bright sun. I've tried shade. I've tried bright days and dull days and I swear every combination in between. I can say from experience that the best conditions to get beautiful rich colour and no glare on your painting is a bright overcast day. What's that? Basically a sunny day with lots of clouds. Colours around you should appear normal, not dull. Shadows should not exist or if they do they have soft edges. Once the edges of the shadows turn hard, it's too bright and you will get glare spots on your paintings.

Position the painting at 45 degrees to the sky, facing the sun (ie north here in Australia, or south for most everyone else).
I think both perfectly upright and laying flat on the ground also work too, but this is the setup I found was ideal for me. Place a sturdy support (helps eliminate shake from small and not so small breezes) at 45 degrees to the sky, cover with a black cloth to reduce color interference, and put the painting on this.

Point the camera straight at the painting.
Fill the camera view with the painting as much as possible. Use every pixel possible! Remember to tilt the camera slightly down to match the angle that the artwork is leaning - this will help minimize distortion. Check in the viewfinder to see if all the sides of your painting are parallel to the viewing edge. If not, your camera is at a different angle than the painting. Fiddle until you get this right. Also, remember to set the tripod up so that your shadow is not on the painting as you stand over it!

Trouble with your artwork looking like a big bulge?
That’s to do with the lens. Use the zoom on your camera to zoom in until the bulge effect disappears and the painting edges are parallel with the viewing edges, while simultaneously backing away from your artwork so it fits the viewing space. Or use a standard 50mm lens.

Camera tips

Use the largest image setting possible for your camera to get the highest resolution images
Set your camera's ISO to its lowest native setting to ensure the least amount of image 'noise' - aim for 50 ISO
If you can, lock the SLR mirror up as this will reduce camera shake as the shutter fires
Use a self timer if you can to eliminate any camera shake as you press the shutter button
Always bracket exposures - huh? Take shots slightly on either side of what your camera says is the ideal exposure as it's not always right for each picture
Don't rely on auto focus to get it right, sometimes a small manual tweak does the trick

Shooting

Shoot the grey card first.
This is to get a standard for the lighting and will make your colour correcting easy peasy. Then shoot your paintings. Try and have some of the grey card in the shot, to the side of the painting too.

Post processing in your digital darkroom, aka Photoshop

Once your shots are off your camera and on your computer, compare them at full size for colour, focus/blur, contrast etc to choose the best one.

If none of the images are quite right, take the time to re-shoot your painting. This is your archive. It's worth getting right. Once the paintings have gone to their new homes it's next to impossible to borrow them back to re-shoot them.

With editing, often you will find that a small increase in contrast is all they need. Sometimes a small amount of colour correcting can go a long way, too. This is where that grey card shot comes in extremely handy. I'm not going to reinvent the wheel - download this free and super helpful kick ass pdf by one Michael King on how to use a grey card to colour correct artwork.

Always save your images as tiff or psd for maximum information retention. Only save them as a jpeg for emailing once all edits have been done as the jpg format is so small because it throws out fine detail information. Always keep a tiff or psd version somewhere so you can archive your image without any loss of information and re-edit in the future.

Useful links to peruse

http://artlinkswap.org/photographing_art.shtml

http://emptyeasel.com/2007/01/19/how-to-photograph-your-artwork-for-a-portfolio-or-the-internet/

http://michaelking.ca/wp-content/uploads/pdf/Grey_Card_Tutorial.pdf

Varnishing Acrylic Paintings

Tuesday, September 21, 2010

Image courtesy of Manzabar

A go-to guide for you to get a clear speedy summary of why, what, how and how long.

Do acrylic paintings really need to be varnished?

If you want them to last in good condition for as long as possible; if you are professional and aim for the best quality in your artwork; if you want your paintings to be protected from light knocks and accumulated dirt over time; then yes, they do need to be varnished.

How long do I have to wait to varnish an acrylic painting?

Until it is dry, is the short answer. To dry and cure fully, acrylics take about a year. If you can wait that long, then that is ideal. They can, however, be varnished after about a month if needs be. And what if the painting is touch dry, sold and needs to be shipped? Varnish is better than no protection. Just remember that this final coat is meant to be thin! A thick coat on a fully cured painting may not cause any problems apart from raising a learned eyebrow, but on a touch dry painting it will significantly retard or even prevent the drying and curing process, with unpredictable consequences.

Can an acrylic medium be used as a varnish? I've got one that's really clear and nice and glossy.

Absolutely not. A medium and a varnish are formulated with totally different aims. A medium binds with the paint and should not be soluble. Mediums are not made to protect a painting from damage, they are made to change the working properties of the paint for your convenience. If a medium is used as a final layer, it binds intimately with the paint and is not possible to remove without accidentally removing paint at the same time, which obviously damages your painting. Clearly this is the opposite of your intention.

Varnishes are designed to be durable, but they’re also formulated to be removable (or at least they should be). Solubility is one of the characteristics that distinguishes a varnish from a medium. When your painting needs a really good clean, it's the varnish that comes off and is actually replaced with a fresh coat. This top coat of varnish is available in matte, satin or gloss and is designed to be tough enough to give some physical protection against knocks, something that a medium is not designed to do.

So the varnish just goes on top of the painting, right?

No!!! Slow down. For acrylic paintings there's actually a step inbetween.

First it's best to apply a slightly thinned coating of a gel medium prior to varnishing. This will protect the paint in case the varnish needs to be removed in the future. Why don't oil paintings require a layer between the paint and varnish? Because oil paints have much harder surfaces than even well dried acrylic paints, and the acrylic paint surfaces are very vulnerable to solvent penetration and even water penetration. Oil paint surfaces are vulnerable too, but much less so than acrylic paints. Why would the varnish need to be removed? Well part of the point of varnishing is to provide a dispensable layer that can be easily removed when it becomes too dirty to clean properly. A layer in between the paint and the varnish means that when the varnish is being taken off, it makes the conservators job that much easier in avoiding taking part of the painting off too.

And what varnish to use? Well there are many suitable varnishes out there for acrylic paints. According to current best practice from a conservation point of view, choose an acrylic solution varnish or the one acrylic dispersion varnish made by Golden. As to how to varnish, you can't go past the instructions from AMIEN, available via the link below.

Linky goodness

An excellent thread on varnishing on a top forum.

More About Artists Canvas - A Final Word

Tuesday, August 17, 2010

Photo courtesy of patrizia_ferri

As the final installment of my investigations into artist's canvas, this time I'm looking at canvas keys, gallery wrapped canvas vs traditional profile canvas and the idea of unstretched canvas.

Previous related posts cover all about painting substrates, all about the types of artists canvas and stretching your own canvas.

Canvas Keys

Some stretched canvasses come with little wooden wedges. What are these for? They are known as canvas keys. They should fit into slots in the inner corners of the canvas stretcher. They are a traditional method for tightening up a canvas that has begun to sag. Unfortunately, they are not a very good method for doing this. Any canvas that has developed a sag should be carefully taken off it's stretcher and re-stretched.

Using canvas keys to take the sag out of a painting risks damaging the painting. It is possible to accidentally hammer the back of the painting if the keys are missed, breaking the paint. Using keys puts a great deal of stress on the corners of a painting which can eventually tear the canvas. The keys will invariably change the shape of the stretcher and it will no longer be square and the painting may no longer fit into it's frame, if it had one.

Skip the dodgy canvas keys. Traditional, but not very smart. Take the canvas off the stretcher altogether and re-stretch it!

This video explains the same information in visual form:
http://www.youtube.com/watch?v=tSLhkuFO3G0

Bracing a Stretched Canvas

A canvas stretcher or strainer is under quite a bit of tension once a canvas has been secured onto it. They are usually made from timber and so are prone to warping under tension and changing atmospheric conditions. It is recommended that they include a cross-bar every 60 cm (or 2 feet) or so in each direction to help prevent any warping.

Traditional Stretched Canvas

A traditional stretched canvas requires framing. The tacks or staples show on the sides of the finished piece. Traditional canvases also tend to have a shallow profile. They are usually only about half an inch thick from the back of the canvas to the front.

Gallery Wrapped Canvas

This is a very modern style of stretching canvas. The canvas is wrapped around two edges of the stretcher bars and secured at the back where the staples or tacks can't show. Often the sides are painted. No visible staples or nails means a neat finish is achieved and no framing is required. Usually this style has quite a deep profile, more than an inch thick from the back of the canvas to the front, though they can also be shallow. The deep profile is the current trend.

Artists love gallery wrapped canvas as their artworks are ready to hang as soon as the varnish is dry. Many art collectors prefer it too as it allows them to skip the often substantial costs of framing. Anecdotally, gallery wrapped canvasses nearly put many framers out of business when it first came out as so many people suddenly didn't require their services. Though if you prefer your art in a frame, as some do, gallery wrapped canvas can be framed if you want.

Unstretched Canvas

It was a revelation to me when I was introduced to the idea of working on unstretched canvas. I was at the exhibition opening of a local artist who had oil pastel paintings on massive canvasses about 1 x 2 m. They were unstretched and looked wonderful.

Depending on your point of view, unstretched canvas is either fabulous or awful to paint on. It has a very different working feel to the drum-like bounce of a stretched canvas. To me it's wonderful and predictable. The give in the surface of a stretched canvas is something I find disconcerting. Different artists, different preferences. I guess it's like working on fabric textured board or paper.

For the artist there are some significant advantages to working on canvas unstretched. There are time savings as no pre-stretching is required. There are financial savings as no stretchers need to be bought. There are space savings as unused canvas can be stored rolled and once painted, can be stacked flat. Believe me, plain canvas takes up a LOT less room than a stack of stretched canvasses. And lastly, unstretched canvas is cheaper to post for a buyer as it weighs less.

For the art collector, unstretched canvas can be presented in a number of already familiar ways. It can be lightly stretched onto stretchers/strainers and ends up looking just like regular stretched canvas. Or it can be framed just like any paper artwork. For extra rigidity, it can be mounted (glued) to board before framing. All very normal procedures for your framer.

The only downside to unstretched canvas that I can see is that someone needs to frame it.

Stretching Canvas

Tuesday, July 20, 2010

Photo courtesy of Anita Thomhave Simonsen

Stretching canvas. All you need to know in one place. Why would you? What do you need? How is it done? (with a selection of curated videos).

Why would you?

Artists are always looking for ways to save money on materials without skimping on quality. Stretching your own canvas instead of buying it already stretched is a real dollar saver. It also allows an artist to have full control over the canvas they paint on and how it is prepared, and to have any size they choose. So not only can it be cheaper, but better quality too!

However, before getting outlandishly excited, stretching canvas does take time, so if you're not quick at it, perhaps buying ready-mades would be less expensive in the long run. There is also the option of having canvas stretched for you by professionals. Obviously this costs though you get the exact specifications you want and can focus on painting, which is presumably what you do best.

What do you need?

Stretcher bars, either pre or home made, to stretch your canvas onto
Canvas to stretch, which is about 2 inches larger all round than the stretcher size
Canvas pliers are useful to save your hands
A staple gun and staples, or nails or tacks and a hammer for securing the canvas to the stretcher
A mallet for tapping the stretcher together
Tape measure for checking the squareness of the corners
T square for chiecking the squareness of the corners
Scissors for cutting the canvas
A razor blade can be handy for removing excess off the edges
Blunt nose pliers or a flat head screwdriver for removing errant staples
Misting spray in case the canvas ends up too loose
Patience

How is it done?

Rather than write up a long winded explanation, I instead sought out a bunch of the most useful videos. There are an awful lot out there and most of them are awful! I've sat through as many as I could stand (about 20) to bring you the pick of the bunch.

A good general introduction

http://video.about.com/painting/How-to-Stretch-a-Canvas.htm

This is a 5 minute video which deals with stretching up to about the 2 minute mark has some neat tips with razor blades and misting sprays.

http://video.google.com/videoplay?docid=-271921060817845354#

Gallery wrapping of pre-painted canvas

http://www.youtube.com/watch?v=QkToBRa-O-U

A leisurely series on making stretcher bars and stretching canvas with plenty of handy tips

http://www.youtube.com/watch?v=t7iRiF1k7s4

http://www.youtube.com/watch?v=qY5-7a6QX8s

http://www.youtube.com/watch?v=nJ5H05A4184

http://www.youtube.com/watch?v=lKey4crHzmc

Gesso vs Primer vs Grounds vs Size - What's the Difference?

Tuesday, May 18, 2010

Preparing to paint - Gesso, Primer, Grounds, Size

Photo thanks to Anita Thomhave Simonsen

Size, primer and gesso. If you're anything like me, you're probably as confused as *** when it comes to these and preparing a surface for painting. Not any more. This post aims to clean away the mud and is a companion post to the one last month on painting substrates. So if you want to know what substrate is usable and whether it requires sizing or priming or both, check it out. This one is about the actual size and primer options. And some of it is straight from the wonderful AMIEN forums. Go check them out for all your technical artist materials questions.

Why Size?

Okay, here we go. Raw canvas, or any oil painting substrate, requires a barrier between itself and the oil paint. This is to prevent the paint sinking in to the surface (makes for terrible colour) and also to prevent the oils in the paint attacking and rotting the substrate (a nasty habit of oil paints).

In the case of acrylic paints, a barrier between the paint and substrate is required to prevent Support Induced Discoloration (SID) which is something that occurs in acrylic paints and mediums only. Many common artist supports have impurities that can discolor a translucent acrylic gel layer or color glaze, and a barrier must be applied to ensure the products stay clear as the films dry.

As an acrylic paint film cures, the water exits two ways: through the surface of the paint and through the back of the support, if it is porous enough. Canvas, linen, wood and masonite are all porous enough to allow water to absorb into them. During this drying process, the water is actually in equilibrium moving back and forth between the acrylic paint and the support. The water extracts water-soluble impurities such as dirt, sap, starches, etc., from the support and deposits them into the acrylic film. The result is a discolored (typically amber) film, with the degree of discoloration dependent on the amount of contaminants deposited and the inherent level of inpurities in the support.

SID contamination often goes undetected. In most cases, the paints applied contain a sufficient level of pigment, thus a strong enough color, to conceal the yellowing. However, in a transparent glaze and especially in thick translucent gel layers, SID becomes quite noticeable. SID can transform the appearance of an Ultramarine Blue glaze into a lower chroma, greenish color. Gesso alone will not stop SID, and different gels and mediums have varying degrees of blocking capabilities.

The acrylic dispersion mediums, paints and primers do absorb and expell moisture for about a year after they are applied -- or less time if the environment is warm and dry. After that's finished the resins coalesce into a more continuous film. They are still susceptible to moisture penetration, but not to the degree that puts them at the same risk as RSG. And it's preventable by coating the finished paintings.

In summary, for both oil and acrylic paints, it is wise to put a barrier between the paint and it's substrate. This barrier is known as size. It is meant to be a penetrating sealer, not a coating. It is therefore very thin, using it is good practice, and it's very easy to do.

Ancient and Modern Size

Traditional size for oil paints is a (disgusting I say) concoction of rabbit skin collagin heated with water. Although this has been used for hundreds of years it is know known by conservators to cause more problems than it solves. How? RSG is hygroscopic. It continuously absorbs moisture from the atmosphere, causing it to continuously swell and shrink. Over time, this constant flexing causes the oil paint on top, which is quite brittle, to crack. In fact, RSG is now believed to be the main cause of cracking in old oil paintings.

Instead of RSG underneath oil paintings, it is now recommended to use a pH neutral PVA or any acrylic medium whose manufacturer recommends it as a size. Please remember that PVA size or acrylic medium does not tighten fabric like rabbit skin glue.

Underneath acrylic paints, the best choice is acrylic medium whose manufacturer recommends it as a size that can block SID - a blocking size. A blocking size will be formulated to inhibit the migration of soluble organic materials from the support through to the ground. Two that are often mentioned are Gamblin’s PVA size and Golden Acrylics’ GAC100. Liquitex makes one as well, as I am sure others do too.

Two coats of size on the front of a substrate are sufficient. They should be touch dry and not cold to touch (which indicates moisture) before the next layer is added.

Why Prime?

Priming is the adding of an absorbent coating to a substrate. The aim is to provide the paint with a porous surface to adhere to. Primer is also known as ground or gesso. It is not size and will not seal or create a barrier to the paint. It does exactly the opposite. It is absorbent and provides tooth, or texture for the paint. It also tends to stiffen the substrate.

Usually two coats of primer is used.

Just for the record, you don't need to prime unless you want the surface that priming gives. You can paint directly onto modern size (but not RSG).

All About Gesso

Traditional gesso

Real or traditional gesso is for hard inflexible surfaces only. It is too brittle for canvas and will crack. Real gesso is like a plaster and is ideal on wood panels. It is made from a thin base of RSG and inert white pigments. The pigment is powdered chalk, calcium or gypsum. Sometimes titanium white pigment is also added to the mix for brightness.

This zinc oxide in the ground is a problem in terms of archival quality. Paint over zinc oxide and within a few years time the painting is likely to be delaminating or cracking.

Modern gesso

Gesso changed in the 20th century. In 1955, Liquitex, an acrylic paint company developed the first water-based acrylic gesso. It provided a consistent and inexpensive primer layer for both acrylic and oil paintings. Technically it is an acrylic dispersion primer, not a gesso, but it is mostly known as acrylic gesso or acrlyic primer. This is the only choice of primer available for use under acrylic paints.

Oil gesso

It's really useful to remember that an oil-primed canvas can only accept oil paints. Although oil paint can be applied to acrylic gesso, acrylic paint will not permanently adhere to an oil-primed canvas. The acrylic gesso will eventually peel off the oil-primed canvas.

Today there are two alternatives to traditional gesso with it's RSG content. There are oil/alkyd grounds which are the quickest drying option. And there is lead white oil primer. The latter is somewhat hazerdous to use. Don't smoke or eat in your studio. Use a barrier cream on your hands or wear thin rubber gloves so the lead can't penetrate your skin. Use odorless mineral spirits to thin the primer, not gum turpentine; odorless mineral spirits is hazardous but not as hazardous as regular mineral spirits and definitely not as hazardous as gum turpentine. In any event, you will want good ventilation when using these solvents: at least work near an exhaust fan. Thoroughly wash your hands when you are finished.

For the lead white oil primer you will have to apply at least 2 thinned coats. Allow perhaps a week for the drying of the initial coating, depending on the temperature and humidity of your studio. If it is dry to the touch after a few days, then you can go ahead and apply the second coat. After you apply the second coat, check to see that the coverage is good. You might want a third coat.

So there are three choices for priming for oil paints. Acrylic gesso and two kinds of oil based gesso.

Acrylic grounds under oils

In recent years, some artists have begun to question whether or not acrylic gesso is the right product to use under oil paint. Acrylic dispersion grounds retain their flexibility as they age, and the oil/alkyd grounds get stiffer and more brittle as they age. There is concern that this difference in flexibility may cause oil paintings on acrylic grounds to delaminte as they age.

The best current knowledge is that they are considered very good grounds for oil paints, with two caveats. 1.) You must purchase the highest quality ground you can find. That means: do not by acrylic dispersion grounds by price, and be sure the label tells you what's in the stuff. If you're unsure about the latter, call the manufacturer. 2.) Oil paints ought to be painted on rigid substrates. If the acrylic dispersion ground is applied to a panel, or to a fabric mounted on a panel, there should be no problems.

For a better bond with oil paint, after the acrylic primer is dry (when it's no longer cool to the touch is a good indicator) you should wipe this surface down with warm water and a clean rag to remove surfactants and allow to dry again (24-48 hrs) before applying oil based paints.

Linky Goodness

Amien forums

Golden Paints technical info

Gamblin & size

Liquitex pdf book on acrylics

Oil Painting Substrates

Wednesday, April 21, 2010

Image courtesy of Takomabibelot

Last month I went searching for answers on the topic of artist's canvas, which has been of use to people other than myself including the lovely Elise who has an exhibition coming up. This month I'm interested in anything but canvas. What else can we paint on and how does it need to be prepared to an archival level? As I also have a personal interest in trying out acrylics in the near future, I investigated for both oil and acrylic paints.

Most of this information has been gathered from the heavily moderated (in a good way) AMIEN forums. The Art Materials Information and Education Network is a non profit that is "dedicated to providing, without regard to aesthetics, the most comprehensive, up-to-date, accurate, and unbiased factual information about artists’ materials. The information is based on the most current scientific knowledge from peer-reviewed sources regarding quality, durability, and health hazards, and on original research conducted at AMIEN. The information is not prescriptive: AMIEN does not tell artists how to make art. We want artists to be able to make intelligent choices about any material used to make art, and we want to help artists make art safely.

Our goal is to reach as many artists as possible, amateur, student, and professional alike as in order to fulfill the mission of AMIEN."

Sounds pretty damn good to me. And it's free.

I should point out that what I have done is gather and interpret the information as best I can and that it is by it's nature, generalised. If you have specific questions I highly encourage you to register on the forums and get expert advice tailored to your situation.

PAPER

Not highly recommended for really dependable durability, but certainly usable for both oil and acrylic if it's prepared right. And that is the key. Just a couple of things to remember: choose archival grade paper such as nice thick acid free cotton rag 300+gsm watercolour paper if you want the painting to last. And there's always Museum board to try too, which is basically archival cardboard. These will need to be protected from the environment by framing behind glass for maximum longevity.

For oils, prepare the paper with two coats of pH neutral PVA size or an acrylic dispersion "blocking medium" to protect the paper from the oil in the paint. For acrylics on watercolour, just paint. Watercolor papers are already sized either internally or with a surface sizing (or both), according to the manufacturer. Other papers would need to be sized.

WOOD

Timber has been used for centuries in the form of panels for tempera and oil paintings. It has the advantage over canvas in that it is rigid and therefore far more stable for the paint. The surface doesn't flex as much as canvas on stretchers which means the paint is more likely to stay put and not crack or peel. Prepared canvas can be mounted on timber instead of being stretched onto a frame.

All timber based products need to be prepared to prevent the paint sinking and the chemicals in the support rising and getting into the painting. It's a very good idea to seal whatever timber product you chose on all sides and edges to help prevent it from warping. Also, if you don't seal the painting surface, the wood just soaks up the paint and makes getting colours right very frustrating. There are some suitable clear sealants out there if you want to use the grain of the timber as part of the composition. Timber substrates often also need to be braced at the back, especially large pieces, to prevent warping.

Solid timber panels

Although used for centuries, there are much better choices around today. Hardwoods are the best choice as the softwoods such as pine are full of volatile oils that like to make their way out and eat your paint. The hardwoods are also more dimensionally stable. Even so, cracking, warping and cupping are a strong possibility.

Solid wood panels larger than about 30 cm square are not recommended. Panels should be as thick as possible, at least over 25 mm thick, and made of the densest hardwood available.

Any solid timber panel bigger than 30 cm on a side needs to be braced. All timber panels should be sanded smooth, sized and primed on both sides and the four edges. More than one coat of primer is best on the sides, but not necessary for the edges.

Masonite or hardboard

Firstly, what is masonite? From Wikipedia: "It is formed using the Mason method, using wood chips, blasting them into long fibers with steam and then forming them into boards. The boards are then pressed and heated to form the finished boards. No glue or other material is added. The long fibers give Masonite a high bending strength, tensile strength, density and stability. Unlike other composite wood panels produced using formaldehyde-based resins to bind fibers, Masonite is made using natural ingredients only".

Actually there are two types of hardboard, tempered and untempered. Tempered is harder and has a less flexible surface BUT actually contains some added oils and silicone. Untempered is the plain stuff. Both are excellent painting supports.

It's worth knowing that hardboard has lignin in it, a naturally occurring adhesive that will cause darkening and should be isolated from the ground and paints. This is more of a concern when using acrylic dispersion grounds and paints than when using oil grounds and paints. Lightly sand then use an acrylic dispersion blocking medium to prevent the lignin from migrating and then prime.

Any hardboard surface over 30 cm (~12") in any direction will need cross-bracing every 30 cm.

Plywood

Plywood is porous and contains natural oils that can cause problems with your oil paints curing process. Good quality plywood is suitable for both oil or acrylic paints if prepared correctly. Do not paint on soft woods such as pine because they contain more resins and do not resist moisture very well. If you're worried about plywood delaminating, remember that newer glues developed in the past twenty years are much better than the older ones. To be safe, go for exterior-grade plywood or marine-grade plywood, whose glues are even stronger and more waterproof.

Prepare by light sanding then coat with a blocking medium and then prime. As usual, large sizes will need bracing.

Mdf and chipboard

Usable but not really recommended. These are basically a wood sawdust or chippings held together by resins and waxes which gets complicated and unpredictable very quickly (read chemical soup).

GLASS

Not a recommended practice. Regular oil or acrylic paints will go on to glass but are less likely to stay on than paints made specifically for glass painting which are fired and fused to the glass. Regular oil and acrylics will tend to eventually peel and chip off. And we don't want that. If you do want to give it a try, sandblast the glass first or rough it up with wet and dry sandpaper.

METALS

Metals are smooth and need to be treated, usually by lightly sanding, to develop a tooth that will accept paint.

Aluminium

Aluminum honeycombed panels are really good to use. Stiff and light. They are an ideal substrate for paint. Acrylic paint, that is. Aluminium and the acrylic have similar reactions to changes in temperature while oil paints grow more rigid and brittle with age and so are not a good choice.

To prepare aluminium, lightly sand the surface. An electric orbital sander is ideal, and wash off the aluminum surface with a bit of rubbing alcohol (70% isopropanol). Remember to wear protective gloves and a vapor mask. Then prime.

Copper

Oil on copper is lovely, but the paintings require a lot of care and a good environment such as a museum for long-term stability. Copper is highly reactive to water in the environment.

To prepare copper for adhesion of paint use an electric orbital sander with a non-clogging paper to thoroughly scuff up the surface and you can also chamfer the panel edges slightly, to inhibit chipping. Wipe the surface clean with denatured ethanol. You MUST avoid breathing the copper dust, so wear a respirator or use a direct local exhaust vent. You SHOULD avoid skin contact with the ethanol, so nitrile rubber gloves are recommended. You should also avoid the ethanol vapors, so your respirator ought to have have both dust and vapor filtration. Then prime.

PLASTICS

Fiberglass

Yes this can be painted on. Fiberglass is essentially a polyester resin with strands of glass fiber dispersed in it. Polyester is very stable, and so too is glass.

Large panels will need to be braced and cross-braced as with all large work.

For either oil or acrylic paints, prime with an acrylic dispersion primer using at least four coats.

Acrylic sheeting

Acrylic sheet can be a suitable substrate for acrylic paints only. Like aluminium it remains pretty flexible as it ages. It expands and contracts with changes in temperature. Brittle paints like oils may have a long-term problem with cracking.

To prepare, thoroughly sand until there is no visible gloss. Apply two layers of acrylic ground to the painting side.

Be aware that you should try to find out if the brand of acrylic sheeting you're proposing to use has any plasticizers in it, and whether the maker knows if a plasticizer in its product might have a tendency to be released. If it does, the sheet might "sweat" from the back. The coatings on the front might block the sweating. You'd only notice this after a long time, perhaps a year, and by feeling the back surface of the panel: it will feel a bit slippery, if you catch it at the right time.
The evaporating plasticizer might have no long term affect on the stability of the panel. On the other hand, the panel might become more brittle and subject to cracking, just like a solid wood panel would.

Also, large unsupported sheets will bend of their own weight and the thinner the panel the more obvious this will be. The sheeting will need a rigid mounting system for around the edges.

Polyester canvas

Polyester is a most durable material. In many ways it is a better choice than cotton duck as canvas. The things to watch out for are coatings or other surface treatments. You don't want the unpredictability of these. Go for pure polyester fabric made for artists' use. Not the thin stuff used for clothing. If the polyester is absorbent and the threads are somewhat fuzzy, a properly formulated ground of any type should make a mechanical bond with it. Both oil and acrylic dispersion grounds will work and both oil and acrylic paints are suitable for use with this substrate.

A Bunch of Useful Links

Painting on glass
Melamine coating problem
Art materials information and education network - pure gold

I can see that the next technical installment needs to be on sizing and priming

Square Brush / Square Touch Brushwork Technique

More art technique articles

Photographing Paintings For Artists Records

What you will need

The photography setup

Camera tips

Shooting

Post processing in your digital darkroom, aka Photoshop

Useful links to peruse

More art technique articles

Varnishing Acrylic Paintings

Do acrylic paintings really need to be varnished?

How long do I have to wait to varnish an acrylic painting?

Can an acrylic medium be used as a varnish? I've got one that's really clear and nice and glossy.

So the varnish just goes on top of the painting, right?

Linky goodness

More art technique articles

More About Artists Canvas - A Final Word

Canvas Keys

Bracing a Stretched Canvas

Traditional Stretched Canvas

Gallery Wrapped Canvas

Unstretched Canvas

More art technique articles

Stretching Canvas

Why would you?

What do you need?

How is it done?

More art technique articles

Gesso vs Primer vs Grounds vs Size - What's the Difference?

Why Size?

Ancient and Modern Size

Why Prime?

All About Gesso

Traditional gesso

Modern gesso

Oil gesso

Acrylic grounds under oils

Linky Goodness

More art technique articles

Oil Painting Substrates

PAPER

WOOD

Solid timber panels

Masonite or hardboard

Plywood

Mdf and chipboard

GLASS

METALS

Aluminium

Copper

PLASTICS

Fiberglass

Acrylic sheeting

Polyester canvas

A Bunch of Useful Links

More art technique articles

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