An Answer to the Question of Longevity...
I have often been asked about the permanence, longevity or stay-a-bility of a coffee based painting. More specifically, "Will the painting fade?"
My response up to this point has always been based upon information I have gathered from the web concerning the use of coffee as a stain for fabric over the centuries, etc. However, I could only state "It should be stable and not fade" unable to be really certain.
Therefore, I decided to seek the advice of a good friend of mine, a chemist with a Doctorate and great past experience in paint formulation and testing. His advice was to setup an exposure test. in other words, to subject the coffee painted paper to the "full on" Florida sun and see what happens.
So, I conducted the following experiment:
I painted six strips of color on D'Arches 300lb rough watercolor paper (the paper I most often use) three colors of which were Winsor & Newton paints and the other three consisting of various intensity washes of Starbucks® French Roast Coffee. After the color washes had fully dried, I cut the paper in half in order to run two tests; a Coated, as well as, an Un-Coated exposure test.
Taking the half that I had designated for the Coated test, I sprayed the entire surface with Krylon brand, "Kamar Varnish" an acid free, non-yellowing, matte finish protective coating formulated for oil, acrylic and watercolor paintings. After the coating had dried completely I again, cut the paper in half.
Next, I took the other original half designated for the Un-Coated test and simply cut it in half again, at which point I now had 4 pieces of paper, 2 Coated and 2 Un-Coated. Selecting one from each set, I taped them to a board (in order to hold them flat) giving me a "Test Board" consisting of one Un-Coated strip and one Coated strip.
The other 2 strips I set aside in my studio, out of the way, in order to retrieve later when it was time for comparing the results.
What I did next was extreme, and something that one would NEVER, EVER do with an original work of art, especially a painting as delicate as watercolor... I placed the "Test Board" outside on my patio, usually around 11:30 AM or so, and then took it back inside around 4 or 5 PM exposing the Coated and Un-Coated color washes to the Florida sunshine for 4.5 to 5.5 hours at a time. I continued this exposure process until I had accumulated 40 hours of direct sun! To compare the results, i realigned the strip sets side-by-side those that had been exposed to the sun's rays and those that had stayed safe indoors.
The results are pretty cool.
Here is the Coated Color Strip Test results
Surprisingly, the most significant color shift occurred in the Winsor & Newton brown toned paint! The Starbucks® French Roast washes, after 40 hours of direct, intense Florida sunshine had only very slightly faded, as most evident in the "Straight from Cup" wash.
Additionally, I found that there was very little effect difference between the Coated and Un-Coated test strips...
Obviously the intent of the coating is to protect from accidental water damage or dirt, etc, as the product DOES NOT state UV protection.