Printing on Al - my experience
I was able to get good prints on Al by the method I describe below. Although I continue to fine-tune the procedure, the set of prints I have are happy outcomes - flaws and all. I am thankful that gum arabic served to increase the viscosity sufficiently to keep the sand flour particles in suspension through the coating steps.
1. CLEANING PLATES:
Clean plates w soapy water (tear drop test for cleanliness).
Clean 3x w 99% isopropyl alcohol.
Mask borders if desired w painters' tape or tackier tape.
2. GROUND PREPARATION:
30 ml of 14 Baume Gum Arabic
60 ml water
Add acrylic gesso (I used Stevenson's) to desired opacity
10 g Sieved Sand Flour
Pot. Dichromate powder equivalent to the concentration used to get shadows to print
(I found 2% more than enough)
3. APPLICATION OF GROUND:
a. Use a dampened, squeezed out roller
b. Pour an aliquot of the stirred ground on to plate and apply it uniformly w roller
IMPT: helps to have roller barely charged. Hold it in a sandwich bag while c and
d (below) are carried out to prevent it from drying
c. dry coat w hair dryer set on hot
d. UV for 1 min to harden entire coat
e. Turn plate 90 degrees and repeat b-d till ground is of desired thickness.
4. GELATIN SIZE:
4% gelatin hardened w HCHO and containing ever clear is applied on 3 consecutive days (allowing gelatin to dry for 24 hours between each application).
5. APPLICATION OF GUM EMULSIONS:
- Use a 10% amm. dichromate stock for mixing w gum and water color pigment
- It HELPS to dampen plate w a wetted, hand-wrung towel before brushing on
emulsion with a dampened, flicked, foam brush to get streak-free spreads.
- dry coat w an overhead fan.
- If, during development of an exposed gum layer bubbles form between the
ground and the Al surface, REJECT the print: the dried bubbles prevent
close contact between the negative and the printing surface during subsequent
gum passes. Rate of bubble formation was 1 in 24 plates in my hands.
6. CYANO PASSES:
Can be done on top of gum. This requires long exposures (~1 hour in the
shade on a sunny summer day).
- If there was any balling of the gelatin when the gum emulsion was applied
(resulting in raised dots that may be colored or white), the cyano emulsion will clear them. In some prints, I found these dots to be a windfall!
I hope the above persuades more gummists to take on Al. Questions or comments are welcome.