December 14, 2010
The first time I began creating paintings on panels using chalk gesso I had no problems. I read the manuals, ordered the materials from a good supplier in NYC and proceeded to create my panels. No problem. It was summer in Connecticut. 30 years on, the paintings I created from those panels are still alive and well.
Over the years, with other batches both in sunny, dry, warm California and later in Germany (also in the summertime), I had no problem. My batches were done using rabbitskin glue sourced from my American art suppliers (Utrecht in NYC or Bay City in SF) or later Kremer pigmente in Munich. Now, after moving to Bruges, I’m back to creating new batches of gessoed panels. But why am I experiencing such difficulty with my gesso? How strange to find myself returning to square one with what should be a relatively simple process. So, I’ve decided to document my trials and errors – for myself and internet posterity. There may be others out there who have experienced similar problems?
My assembly process would begin normally, but as I proceeded to build up layers, the gesso would no longer flow but rather glom onto the panel. The brush would stick, the gesso would glob. When dry, a little sandpaper would remove far too much pigment. So it was clear: there was a problem with my glue.
I generally create my panels in the wintertime. Nothing to be done about that. The house is radiator heated, that’s got to be better than whatever (winter) conditions Cennini ever experienced. We live next to a canal in an older house that does not contain double glazed windows, so it might be more drafty and moist than many modern environments, still, creating good gesso panels should be possible.
Double boiler? Yes, of course. Did the glue boil? No. Never. But after the gelatine melts, what is the threshhold temperature which spoils the glue? I researched temps on the internet and found 52° Centigrade to be the most generally noted gauge. But is that true? From my experience, it depends on the source, as RS can vary a great deal. At this point, I would not go by numbers but rather my own eyesight.
For example, a few years ago I bought a new batch of glue from my local art dealer, a man who specialized in esoteric artists materials. It seemed OK at the time but then the problem began to recur. Does RS have a shelf life? Or did I let the glue “cook” too long? I had purchased a meat thermometer and kept my temp well below 52°. Still, invasion of the glom.
For my most recent batch I used the last of my old RS from the esoteric art supply store. When I added the pigment, the paint became very granular and unattractive. I guess it does have a shelf life (even though it did not smell)… So I threw it out.
Then used the RS that I had purchased recently from Kraemer Pigmente. Little crystalline pebbles, very nice. When I ran out of the Kraemer RS (silly, I had only purchased a 100 G test amount), I bought a new batch of glue from my local art supply store (brand, Senellier). This stuff comes in pellets similar to the scat of small animals that you might find in a forest. (I prefer the Kraemer) But for both glues, I soaked them overnight (80 G RS to 1 liter of water), melted, cooled and did the finger-pressure-crevice test. So far, so good. (Though the Kraemer RS seemed firmer, clearer, less cloudy, more uniform and refined.)
I bought an electric warming plate at the local Kringwinkel (Salvation Army). It holds food warm but doesn’t cook it. 40° Centigrade or so but not higher. Great, I thought. But still, when I kept the glue-pigment in that double boiler pot for a few hours, the glue lost its strength. Oooops.
- Buy the best grade of RS that you can find from an archival artist’s materials supplier (like Kraemer).
- Do the crevice test, if you want, but be sure to take it off the heat as soon as it fully melts.
- Add your pigment in the center in a stream, allowing it to gently absorb the glue and sink via gravity.
- Stir thoroughly but not vigorously.
- For uniformity, do your gessoing in one session (one day).
- Rabbitskin glue is an organic substance, containing all the resilience and receptivity of living matter, as well as it’s limitations.