For most of us, it isn't worth going to extreme lengths to make our paintings as permanent as they can possibly be. You could, for example, choose to paint on high-tech aluminum honeycomb panels. These are light, long-lasting, and much better supports for painting than most of those used by artists, because they don't significantly expand or contract with changes in temperature and humidity. They also cost hundreds or thousands of dollars. If you know that you are a visionary artist who will be producing work of breathtaking magnificence that will be of incredible historic significance, you owe it to future generations to eat only cheap prepackaged noodle dishes at each meal so that you can afford to paint on the most permanent and expensive supports (until you work starts to sell for many thousands of dollars—then, go ahead and treat yourself to a nice juicy tofu burger).
For the rest of us, not so much. Most paintings by even fairly good artists won't be saved for much more than a generation. The best way to preserve your paintings is to make them really, really good (or really, really popular, which 20th century artists demonstrated to have no correlation with good). A painting that people like a lot will be hung on a wall in a room that has a reasonably constant temperature and no wild swings in humidity. Almost any painting will survive for a long time under those conditions. And if people really like it, it might hang in a museum or get restored by a conservator if it starts to show signs of wear and tear. If a painting isn't that great, then even if it's made with excellent crafstmanship and highly archival materials it's likey to be kept in the attic, basement, or garage for years at a time. Even well-made paintings won't last long under those circumstances, and when they start to fall apart, no one will pay for a conservator to fix them. So the most archival quality a painting can have is to be so well-liked that the owner (and the owner's heirs) could never imagine putting it in a moldy basement.
(Of course, if you are a very famous celebrity such as Sir Paul McCartney, your incredibly bad vanity paintings will be treasured and preserved for centuries. Go figure.)
Nevetheless, I think it's a smart to construct paintings with quality materials and good craftsmanship, if only so that customers won't complain until after you are dead. Here are some guidelines for oil painting. If you don't follow them perfectly, it won't cause your painting to explode. But the closer you adhere to them, the more likely your painting will be to last a long time under optimal conditions, or survive brief periods under poor conditions. If you want a painting to last a long time under poor conditions, oil paint is a very bad choice of medium.
- Rigid supports are better than fabric supports. Fabric is flexible, and every time it flexes (as it will do when temperature or humidity changes) the bond between the support and the paint is affected. Over time, that's very bad for a painting. Copper, steel, and aluminum panels are excellent supports for painting (although they can be heavy). Wood is OK only if it has been seasoned for a year or two after being cut and planed to size. Hardboard is probably OK if there is a good barrier between the panel and the paint. Tempered hardboard is stronger than untempered and that makes it better (despite what some sources say) even though there is a slight amount of oil in the surface of tempered hardboard. Medium density fiberboard is OK only if it is very well sealed on all sides against moisture.
- It may be that polyester will turn out to be the most archival fabric, because it is more dimensionally stable than organic fabrics like linen and cotton. We don’t know yet.
- Oil grounds are good to paint on. Lead grounds are the best oil grounds, because lead is a very flexible pigment. Acrylic primer ("gesso") is probably a decent ground to paint on (we'll know for sure in 100 years) but murder on brushes. Traditional gesso is probably an OK ground on a rigid support (the hide glue in gesso is very strong, which is good, but likes to absorb water, which is bad).
- Use permanent pigments. Alizarin crimson is not permanent, especially in mixtures and when applied very thinly. Impermanent pigments will fade or become dull over time.
- If you use linen, cotton, or hemp as a support, don't put paint or oil primer directly onto it. The oil will rot the fabric. You need a barrier, such as hide glue or acrylic primer, between the paint and the fabric. Make sure the barrier covers the sides as well as the front of the canvas.
- Don't apply a lot of thick paint. Thick, heavy layers of impasto are much less permanent than thin layers (about the thickness of a layer of house paint). Several thin layers (allowed to dry in between) are much more permanent than one thick layer. A few expressive blobs of impasto here and there are not going to cause problems, but large areas of thick paint are bad.
- Linseed forms the strongest paint film of the drying oils. Walnut is less strong. Safflower and poppy are weaker still. Because the same stuff that make the paint film strong also yellows, linseed will yellow more than other oils. But go for a walk through a museum with paintings three or four hundred years old. You probably don't find yourself thinking, “Wow! those paintings now suck because they've yellowed.” (Ignore Brown School paintings from the 17th and 18th centuries that were deliberately painted with an overall dull yellowish tone.) You can barely notice the yellowing, and those paintings were almost all done in linseed. Whites are a little warm, blues turn slightly greenish. That's how bad the yellowng gets on a well-made painting. It's barely noticeable, although some paint manufacturers will try to scare you into buying special “non-yellowing” paints made with oils that are less strong. Personally, I only use paints made with linseed and, to a lesser degree, walnut. I avoid paints made with poppy and safflower. If you do use safflower oil, be aware that the kind you can get in a grocery store is almost certainly not the kind that dries properly when mixed with oil paint.
- There are a number of good reasons to avoid student grade paint, but archival permanence is not one of them. Student grade paint from a good company will be as archival as their artist-grade paint.
- It is best to not add anything to your paint—no mediums, no solvents, no nothing. If you do add stuff to the paint, add only a little bit (less than 20% of paint volume). If you add solvents, don't make the paint watery or washy, just add enough to make the paint more manageable. If you apply a layer of medium to the surface of a dried layer of paint before you paint over it, make it a very thin layer.
- It is best not to add metallic driers to make the paint dry more quickly. If you do add them, I think that lead napthenate is best. Add a tiny amount (like one drop from a toothpick) to a penny-sized blob of paint on your palette. Add driers only to the slow-drying pigments on your palette.
- In my opinion, it has not yet been demonstrated whether alkyd painting mediums (Liquin, Galkyd, Neo-Meglip, and so on) are sufficiently permanent. They are probably fine for single layer, direct painting. I’ve heard a couple of complaints about delamination in multi-layered paintings that may be due to use of alkyds. Some alkyd mediums can also yellow quite a bit. Personally, I don’t see any reason to paint with anything that smells like that.
- If you add solvents and oils to your paint, and you work in layers, it’s best to follow the fat over lean rule. That just means that no layer should have less oil in it than the layer beneath it. So be careful about how you use mediums and avoid painting large areas of lean paints (without much oil in them) like manganese violet over large areas of fat paints (with a lot of oil in them) like ivory black. The fat over lean rule is especially important if you paint in thick layers. In thin layers, it’s still a good idea, but less crucial.
- Varnish the painting after it is dry. By dry, I mean three months to a year after completion, depending on how thick the paint is.
Personally, I doubt that the art conservation robots in the Louvre in the year 2306 will curse my name because I used sub-standard methods requiring them to spend an extra 324.663 seconds fixing one of my paintings. But that would be really cool.
Update 10/23/06: One other point regarding how to construct paintings that will last. If you paint in multiple layers, make sure that each layer adheres to the one below it. A paint layer that is smooth and shiny is not a good surface for painting over, because the next layer of paint has no mechanical tooth to adhere to. You may want to scuff up the surface with a green kitchen scrubee pad or, if you prefer, wet sand. If you use a medium that contains a balsam such as Venice turpentine or Canada balsam, the paint will adhere better to the previous layer.