This topic is under debate. We believe much of the controversy is due to using the wrong acrylic primer or paint system, under an oil paint that additionally may have been applied in an incorrect manner. Here is our suggested method to ensure a proper bond between oil and acrylic.
First, it is our belief if the oil painter is concerned with creating artwork that will last for as long as possible, the artist should first select a rigid support such as birch plywood to either paint directly on, or stretch a canvas over and secure it. We don’t think anyone will debate an aged oil paint film is going to crack if flexed, so why give it the opportunity? The use of a panel also ensures less exposure to moisture from the backside of the canvas. Not only does this reduce the chance of swelling of acrylic polymer or rabbitskin glue sizing, but it prevents the elements from breaking down the fibers of the fabric. Secondly, The surface should be properly sized according to the kind of paints and how these paints are going to be used.
Rabbitskin Glue is used traditionally as a size for oil painting as it reduces the ability of the acids in the linseed oil from coming in contact with the fibers. If allowed the acidic nature of linseed oil will break down the fabric causing it to crumble.
Acrylic polymer mediums such as GAC 100, have been tested for preventing oil penetration and for a phenomenon called Support Induced Discoloration (SID). When the GAC 100 is applied sufficiently, typically 2 brush coats, it prevents the oil from penetrating and it greatly reduces SID in acrylic paints and mediums. SID is when water-soluble impurities such as dirt or glues in the support are pulled into the acrylic film during drying. This causes a discoloration such as yellowing, that is most pronounced in glazes or straight gel layers. The use of an acrylic size also ensures the beginning of a bond between the support and subsequent priming/paint layers.
Third, use a quality primer. Acrylic gesso comes in many forms. Some artists will skimp on materials at this stage and use either a student grade version, or even house paint. Some gessos on the market may also be too thick or too glossy to be of great benefit to the artist. Others, usually bargain gessos, have an overload of solids and are under bound. The resulting film simply isn’t a durable film, and is most likely very susceptible to moisture. If a poor grade of gesso is used, it won’t matter how great the paint is; the entire painting layer is at risk of delamination. A proper gesso or primer, needs to have certain qualities to ensure long life of an artwork.
It needs to be thin enough to penetrate the weave of the canvas. It needs to be made with a proper solid to binder ratio. The solids used must generate the proper tooth to sustain a “Lock and Key” effect for the paint layer. If the subsequent paint layer, regardless of whether it’s oil, acrylic, or whatever, isn’t being applied in a lock and key manner to bond the two layers together, the layers may separate over time.
Additionally, the acrylic priming layer needs to have been fully cured before painting with oils or alkyds. Although acrylics dry very quickly, many people assume they are cured when touch-dry. Acrylics actually can take several days or even weeks to cure to the point where all of the water and additives have escaped the film.
In acrylic paintings, the curing time isn’t as critical because the priming and paint layers are similar. But because there are two very different chemistries involved between oils and acrylics, it is paramount you do everything possible to make sure these layers are interwoven, and sufficient time has been allowed for proper curing.
Fourth, oil paint application is important: not only to achieve the proper primer and paint bond, but also because it’s vital to the life of the painting. There has been much discussion of the kind of oils used in paintmaking and medium use, but we have not seen much about the proper oil painting fundamentals. Perhaps many have taken these for granted that everyone knows them. Fat over Lean. Slow drying over fast drying. Thick over thin.
The chemistry of oil paint demands these principles be followed, or suffer the consequences. We believe many artists have long forgotten these things, or worse, they have never been taught them. To me, this is just as important to creating long lasting artwork as the priming.
Oil paints have been used for a long time, but there has been a lot of conservation done to keep most of the great works viewable. There is a lot of recent artwork in oil that is only a few decades old and requires great attention. Ask any conservator.
Fifth, varnishing is important. Varnishing isn’t just for you to get the final sheen you desire, although it is one function. Varnishing is meant to protect in the long haul of things. A good varnish job does not detract from the artwork and goes on almost invisibly. This layer is going to protect your artwork when we’re all long gone. Varnishes are removable coatings and many have Ultra Violet Light Stabilizers to slow fading down.
Finally, paintings need to be in a good environment during their life. If it’s meant to last, humidity and temperature fluctuations can spell disaster. You may not notice it in the next couple of years, but in the long haul, this leads to premature cracking, cupping and then delamination well before the materials can endure. This has been long-winded, but we think the question goes well beyond “Can I use acrylic primers under oils?” The answer is not a simple yes or no, as there are many factors to consider.
