Bonding and sealing
March 14, 2014
Catherine Campbell writes, "I have a varnish dilemma. I've almost finished a commissioned acrylic painting that
I will be bringing back from Mexico to Canada in a few weeks. I wanted to put a coat of gloss medium over that work before we leave, to seal and protect my work of 2 months from airport inspectors' hands. I asked an artist friend travelling through the USA to pick up some medium for me, but they brought Liquitex Gloss Medium/Varnish. It says that it is acrylic polymer emulsion. If I use it, can I still paint on it, or put my more matte varnish over it when I get home?"
Yes, you can, Catherine. Both Dad and I have a system of applying medium, diluted with equal parts water, over finished acrylics and then leaving it to bond with the paint for 24 hours before final varnishing. An isolation coat of medium between layers of paint in progress is good too, for when you're on the move.
Ideally, bonding and sealing require two different actions. Bonding is the thing you do with acrylic medium. Medium is the same molecular product as the stuff that's holding your paint pigment in polymer suspension. The molecules hold onto one another, giving strength and flexibility. Sealing, on the other hand, involves covering the finished work with a protective barrier, lending it further archival integrity with ultraviolet filters (generally referred to as UVLS -- ultraviolet light stabilizers), and the ability to be wiped or dusted. Final varnish should be a removable product, so in the future the painting can be cleaned, repaired or reworked.
The comprehensive Liquitex website explains the many uses and versatilities of each of their products. Their Gloss Medium/Varnish is described as an "all purpose medium, formulated to be mixed into all Liquitex acrylic paints and mediums" -- a breathable, flexible, transparent medium, extender or ground for acrylic paints. It can also be used as a non-removable varnish. The catch here is that it's non-removable. In my opinion, I'd leave your final varnish to a separate product, and do it when you get home. By the way, leaving your matte or satin finish for the final, varnishing stage is the best way to keep your colours clear, avoiding multiple coats of matting agents that can sometimes make colours dull or milky.
PS: The expectations of life depend upon diligence; the mechanic that would perfect his work must first sharpen his tools. (Confucius)
Esoterica: One afternoon while removing varnish by applying a splash of sudsy ammonia to an old acrylic, I watched a pleasing rendering of a Tyto alba break up before my eyes. I ran for the garden hose, and sprayed, thinking I could save him. Instead, he disappeared entirely. It seems I had varnished the painting and later decided to add the owl. With my previous amateur move, I had lost him forever. After the bonding is done with the medium, the sealing with final varnish is but the final kiss. Removable final varnish needs to be properly removed before adding owls.
Robert's health update:
Recent bloodwork showed increased levels of cancer markers since the previous time, but still not as high as when first detected. The cancer in the pancreas seems to have stabilized, but cancer in the liver and lungs has increased in size to some degree. Robert, his family and doctors have decided to stop chemotherapy by injection for the time being and have begun a new strategy of chemo by pills. We have also upped his dosage and frequency of pain pills. Robert is remarkably cheerful painting (horizontally) and writing, limiting guests and unfortunately tiring by late afternoon. His paintings are currently limited to smaller works. Your warm and encouraging comments and messages are especially appreciated by all of us, and we regret our inability to respond to all.