Hi,
I have a couple of questions about preparing wood panels for an Acrylic dispersion prime coat (Golden Gesso). I will ultimately be painting acrylics on top of the primed panels.
1. I have purchased the Zinsser bull’s-eye shellac (yellow label), But then spoke with a materials specialist at Golden and was recommended Midway Polyacrylic. Does you know if one is better than the other for a wooden panels? Can I use either with success to prevent checking and SID, while reducing warping due to changes in humidity? I have listed ingredients of both materials below. If neither would be appropriate, can you please recommend a consumer brand?
* I am no longer using GAC 100 or Gloss Medium to seal wood prior to acrylic dispersion. Recently, Golden came out with information stating that tiny cracks occurred through the acrylic dispersion when wood panels were coated with these materials. For most acrylic painters it is not significant, but I want flexibility and assurance that I’m not going to have fine cracks if I decide to paint thin layers in some areas of my painting.
2. The materials specialist I spoke with at Golden recommended a “spit coat” diluted with alcohol. Do you know what type of alcohol to use to dilute either brand and what the ratio would be for the spit coat?
Ingredients:
1. Bulls Eye shellac:
Ethanol, ISA propanol, methyl isobutyl, ketone, pure shellac, water
2. Minwax polyacrylic:
ISA propanol, 2 – Butoxethanol, dimethyl ether, Hydrated silica
Thank you for the clarification! This was incredibly helpful. One more quick question… For the back of the panel, do you have a favorite brand to recommend of either use shellac or Polycrylic? I have the Bulls Eye, but I didn’t realize it was a top coat. Would it still work, or should I invest in something different? Thank you again for your help and time! This was exactly what I needed!
Hello,
I’m also a material Specialist at GOLDEN. Wondering if there are a couple different conversations that got mixed together here. In general, we don’t recommend either of these products under Gesso as an acrylic painting preparation. if you are planning to paint on panel with acrylic only, our standard recommendation is one or two coats of Gloss Medium or GAC 100, then several coats of acrylic dispersion ground (Gesso) to provide a bright white surface for your acrylic painting. This should help reduce or eliminate the potential for SID and provide a good foundation for your acrylic layers. We have not seen cracking develop in Gesso layers over either of these products. That said, surface checking is a real phenomenon that can affect artworks on plywood. Unfortunately, we do not have any products that will keep plywood from checking over the long term and it is unlikely that shellac or Polycrylic will prevent checking either. Medium Density Overlay (MDO) is plywood with a resin embedded paper surface that should mitigate any issues with checking. It can be prepared the same way as traditional plywood. Adhering paper or canvas to the surface of plywood is another option.
While it might be possible to apply a spit coat, or very thin layer of shellac onto the surface to reduce absorbency of a panel, we are not sure it will reduce SID enough to make that layer worthwhile. Also, thicker layers of shellac are at risk of reactivating if coated with Gesso or other acrylic products. The amines and/or ammonia in acrylics can cause shellac to soften, which is its own issues. It should be fine to use shellac or Polycrylic on the back of a panel to reduce permeability and help balance tension with the layers on the front.
We did recently come out with an article about using oils over acrylics, which may be where cracking came into the conversation. In our testing we saw the potential for lean oil paint to crack upon drying, when used in a specific thickness over certain types of acrylic products. We did not see any issues with oils over Acrylic Gesso when it was used to prepare canvas or panel on its own, but we did see cracking in the oil layers when used over GAC 100 or Gloss Medium. The cracking was in the oil layers only. The Gesso or acrylic layers did not crack in any way. If preparing panel for oil painting, we recommend 3 or more coats of Acrylic Gesso directly onto canvas or panel which can be followed by Oil Ground if desired.
Sorry for any confusion. I hope this helps to clarify.
Greg Watson
Materials Application Specialist
GOLDEN Artist Colors
