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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Medium and Pigments

May 18, 2009

Pigments ground into an appropriate binding medium create paint. The medium defines the paint: the handling (brushwork and siccative qualities), viscosity, translucency, toxicity and permanency. Oil paints are pigments ground and suspended in linseed oil, as acrylics are pigments ground and suspended in acrylic resin. Watercolors are pigments suspended in gum arabic and egg tempera is pigment suspended in the yolk of a fresh egg. Encaustic uses resinated hot wax, while for fresco the setting of the fresh plaster creates the permanency of the water diluted pigment.

Quite naturally, the medium has it’s own qualities which then become a matter of personal taste, capacity or preference. Oil, acrylics and encaustic as mediums, leave a tactile residue of their own quality. Does that quality resonate within you? Find out! All mediums require a support, as for some like watercolor or fresco the support plays a critical, essential role. Do the qualities of the support resonate within you? Find out!

Most modern artists don’t need to grind their own colors to practice their art. However, for the artist working in fresco or egg tempera contact with the powdered pigment is essential. In addition, knowing which pigments to use for which medium is critical not only for successful in-the-moment-handling but also for longevity and personal health. Manuals like ‘Artist’s Handbook of Materials and Techniques’ by Ralph Mayer or Max Doerner’s ‘The Materials of the Artist’ are time honoured general resources. Daniel Thompson’s ‘The Practice of Tempera Painting’ is probably the best comprehensive resource for the tempera painter. Each pigment has its own nuances of hue, saturation and value, also transparency and opacity. Getting to know both mediums and pigments qualitively is a real and exciting adventure. At makingpaint.com you can find extensive information from another working and experimenting artist.

Finally each medium defines its pallette. Fresco due to the chemical interactions of plaster and pigment offers perhaps the most limited choice, while oil may offer the widest. Becoming familiar with pigments and mediums up-close-and-personal is like becoming a master chef. You choose the ingredients based upon experience and a good cookbook, but it’s the attention to detail in the processing that determine a truly successful dish. And who doesn’t enjoy a well prepared meal? Should we treat our eyes with any less care?