Since the glue used is moist, the process is referred to as “wet-mounting” and is not considered as archival as the dry-mount tissue/press process described in the previous blog. While the dry-mount method is reversible with the application of heat, the wet-mount method requires water or other solvents (depending on the glue) to be reversed (Check individual product information for specifics). Since a pastel painting could easily be damaged with the application of a wet product, it becomes nearly impossible to reverse the mounting process, producing a permanent outcome. For this reason it’s of the utmost importance to utilize the highest archival standards possible.
For the substrate, I recommend 100% rag museum board because of its porous surface, which has a better chance of bonding to the adhesive. Avoid foam board, even if it’s acid-free, as it’s easily dented and damaged. If you choose to use another surface, check its PH and acid content before proceeding.
For the adhesive, you’ll need a glue that’s PH-neutral and acid-free to prevent corrosion. Two adhesives I have used with success are Vacu-Glue 300, from Seal Company, and PH Neutral PVA, a Lineco Company product. Both are reversible with water. I’m aware of other artists who use acrylic gloss medium which, once dry, is impervious to water. With acrylic medium, you must work quickly to get a good bond before it has a chance to dry. Note: with heavy water-based underpaintings you should limit the amount of moisture placed on the surface. This is especially crucial around the edges, which easily wick water, releasing the bond. Otherwise, an adhesive that is not water-soluble (like acrylic painting medium) may be the best choice. (In the photo above, you can see my setup of supplies for mounting Wallis pastel paper to rag board.)
The procedure works this way: Cut the pastel paper to the desired painting size and the mounting board a little larger; this allows for positioning without being overly precise. The boarder makes for easier handling and attachment to a rigid support, adding stability. The excess boarder may be removed with a sharp X-Acto knife after the painting is complete. Place the pastel paper upside down on a disposable surface like newsprint (which needs to be discarded after every preparation to hinder glue contamination of the painting surface). Apply the adhesive liberally to the back of the paper with a brush. Keep this application as wet as possible until the paper is adhered to the mounting board; otherwise, a good adhesion may not occur. Carefully flip it over and position it on the mounting board, applying gentle pressure to the center and then working your way out toward the edges. If glue seeps along the edge, quickly wipe it away from the pastel paper so that it doesn’t affect the pastel surface. A rubber printmaker’s brayer or similar device can be handy for this part (make sure no glue gets on the surface of the roller). Lay the mounted paper on a hard flat surface and apply weight; I use a large, smooth sheet of hardboard with gallon cans of paint placed on top to add weight. When doing multiples, stack one on top of the other and leave to dry overnight. The next day, they should be ready to use. If curling occurs due to shrinkage of the adhesive, tape the mounted paper to a drawing board before painting. When completed, framing should keep it flat. If curling is severe, flip the mounted board over and apply a coat of acrylic gesso or similar acrylic product to the back. When it dries, the board should be considerably flatter.
Many of you may have come up with similar or even better procedures; what is of the utmost importance is to create an archival surface by utilizing acid-free, PH-balanced products. A lot of money can be saved by mounting pastel paper ourselves, but it does impose on precious painting time. Allow for experimentation with the process before producing that masterpiece. With practice you’ll have it down to a science and reap the benefits of a perfectly flat rigid surface.
Richard McKinley is a columnist for The Pastel Journal. See his latest article in the current February issue.