Disappointed with the effect fixatives have on pastel images, I tried to make my own. I tried two Casein-based solutions,
"F" : approx. 3% solution of Schmincke's casein solution "Kasein Bindemittel"
(doesn't say what solvent is used), which I diluted with Isopropyl alcohol, and
"P": Guardi "Kaseinpulver fuer Boraxkasein", which I dissolved in warm water
and Isopropyl alcohol (took forever to dissolve, and eventually clogged my mist-pump).
Originally, I weighed out powder for a 3% solution, but the powder didn't dissolve
well in the isopropyl alcohol; I added water and heated the goo for a better solvency,
still took a long time. Solution percentages uncertain at this point.
The first results are in:
The horizontal strips on both sides are untreated, the middle strip is sprayed with "Schmincke Fixativ fuer Kohle und Bleistift", made of bleached Shellack and solvent.
The other two strips are sprayed with the F or P solutions as labelled above.
The "P" strip, made with a water/isopropyl solution causes the most bulging of the underlying paper. Both the commercial, and the solution of fluid casein and isopropyl alcohol alone, didn't cause any warping.
The commercial fixative from Schminke has the best "hold" on the pastel pigment, but is noticeably darker than the rest. My two solutions are less discoloring, but also don't have as good a "hold". (However, they hold well enough that the pigment doesn't fly off the paper by itself.)
I was unable to spray exactly the same amounts, as this was done manually and erratically, from self-primed mist-sprayers. This in itself may explain the difference in the darkening and hold.