Troubleshooting Chalk Gesso

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?

The problem:

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.

Troubleshooting:

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.

Bottom line: 

  • 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.
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Gesso

May 9, 2009

Various recipes exist for gesso. Here’s what I use:

The Glue:
Dissolve 2 3/4 ounces of dry rabbit-skin glue with one quart water in a big glass jar (used pickle jars are great for this). This equates to 75 grams dry glue to approximately one liter of distilled water. The proportions work out to approximately 10/1 water to dried glue by volume. Many professional egg tempera painters suggest a higher percentage of 16/1. (I will try this next time around.)

Let it soak overnight.

Heat the glue in a double boiler, that is, with a second pan surrounding the jar with the glue water. The water should be the same temperature as the glue water, so bring the heat up slowly to melt the gelatine glue. Stir gently. The glue should never boil, only melt. Overheating significantly harms the adhesion of the glue, so do not let the temperature rise above 135 F° (57.3 °C), 127F° (53°C) is optimal.

The Filler:
Use calcium carbonate or precipitated chalk or whiting for filler with 10% titanium white or zinc white to insure a bright whiteness to your gesso.  The chalk whiting part can vary in both purity and whiteness, depending upon the grade. Industrial grade chalk whiting can be found in most hardware stores or paint shops. Dry pigments can be found at art supply shops or online suppliers. 

The proportions are 1 lb filler (or 450 grams) to one quart (liter) of glue water.  Or 1 1/2 filler to 1 glue water by volume. The melted glue is gently poured into the chalk stirring all the while.  Lumps should be stirred or strained out (cheesecloth).  The final result should be about the consistency of light cream.  Return the mixture to the double boiler, to keep it warm but again, be careful not to let it boil.

Applying the Gesso:
Sand the panel lightly to remove any rough texture, clean the dust off with a moist cloth.  Cover the board with a light coating of size (1 1/2 oz rabbit skin glue dissolved in one quart water or 45 grams glue to one liter).  After the size has dried, begin applying thin coats of gesso.  The first coast is loosly brushed or scumbled in. I prefer to apply the gesso to both sides and ends of the panel to avoid the uneven absorption of moisture that can cause warping. I use a wide flat bristle brush, applying thin layers in alternating horizontal and vertical layers.  The layers dry quickly, especially in warm weather.  Generally a well prepared panel can take about 10 thin coats of Gesso. I wait until 3 or 4 levels have accumulated and begin lightly sanding it down between layers, and then using a moist cloth to remove all dust.

Finishing:
After the final coat, the sanding moves from coarse to fine.  As a last step, it’s possible to take a slightly damp cloth and rub it gently over the entire surface in circular motions in order to obtain a final smooth, egg shell-like finish.  If, however, the intended underdrawing will be in silver point, it is best to leave that last step out in order to retain a slight tooth to the panel.