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Wednesday, April 21, 2010

Oil Painting Substrates

Oil Painting Substrates
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


More art technique articles

This article is one in an ongoing series of technical articles for artists, all archived together and accessible from here. The topics range from details on materials, to the business of art, to specific art techniques. Please make use of this resource.




2 comments:

Robert Mayes said...

Hi, There,
I work in oils mostly, and was in a salvage place where I found five large rolls of vinyl wall covering with fabric backing. The backing resembles fine canvas, and seems very regular and ideal as a painting surface. I bought all five for $20, in the hopes of being able to stretch them and paint on them (fabric side for paint surface). I intend to prime the painted surface with gesso. Based upon your experience, what would your primary concerns with this as a substrate be? Ever heard of this being done?
Thanks,
Robert

Fi - WhereFishSing.com said...

Robert,
for truly expert advice tailored to specific situations, I highly recommend the Amien forums where conservators and painting professionals can answer all sorts of gnarly questions like this one.
http://www.amien.org/

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