Preparing Al sheets; other factors
Loris, Keith and Katherine:
Experience of a local artist who paints on PREPARED AL SHEETS:
- sand the sheet with gritty sandpaper
- clean it thoroughly with rubbing alcohol
- brush-coat with diluted gesso
- to change white of gesso, add acrylic paint of choice to it before coating
(Sanding after gessoeing would destabilize the surface, leaving fine dust on top of which would sit the gelatin! How can the emulsion hold on to that?)
I might explore the use of FINE DUST from a dealer who manufactures STONE & GRANITE monuments to see if the white in the gesso can be subdued and the porosity of the topmost layer increased. I will compare the outcomes by adding dust to gesso and/or the gelatin layer before printing. In my first print (Mar 19, '09), I had mixed CaCO3 with the diluted gesso before brush-coating which left visible streaks. I have not been able to locate a source for PUMICE yet. Loris, your idea of using fine activated carbon is interesting. Will await your experience.
As Keith suggests, it might be worth DILUTING THE PREPARED GESSO to reduce its viscosity so brushing it on will not leave streaks.
POROSITY may be a key factor in getting colors from repeated gum passes to merge/blend as they do on paper media and gelatin might provide this. And of course, good TOOTH is vital in preventing emulsions from washing off.
Katherine, I work with a single negative only (no color seps). Additional negs are rarely used if I have printing problems with the single neg. I usually adjust ratios of ingredients in the gum emulsion, exposure times, AD concentration, allowing for dark reactions to occur before or after exposure, etc. Trial and error ad infinitum!
Pardon this long story but hope it answers some issues we have encountered and raises more!!