The problem with trying to print (and not just tone) using salts of gold prior to Mike Ware's development of the new Chrysotype process was the annoying tendency of the gold to precipitate out of solution when the components of the sensitizer were mixed together, using the traditional photoreactive compounds such as ferric oxalate. It seems that the "crux of the biscuit" (Zappaism, sorry) in this process is the introduction of a suitable ligand to hang onto the gold and keep it in solution long enough for it to be coated and dried. Without a more complicated discussion of ligand chemistry, all we need to know here is that the compound is 3,3'thiodipropionic acid (or 3,3'thiodipropanoic acid in Britain- same stuff) and that we need to use its disodium salt. Mike, who seems to be a fan of ammonia based systems has chosen ferric ammonium oxalate as the light sensitive compound, available from Spectrum Chemicals. Get the ligand from Lancaster Chemicals, or both soon from B&S.

The sensitizer can be compounded into three stable aqueous solutions which are then mixed together in equal amounts just prior to coating.

Part A of the sensitizer is the gold component. It is made by taking a 0.9M solution (35.4%) of gold chloride (HAuCl4.3H20) and adding to it slowly an equal amount of 0.9M (3.6%) solution of sodium hydroxide.

Part B is the ligand, and is at a concentration of 1.25M. We want the disodium salt of this ligand so take 100ml. of water (all distilled here) and add 9.0 gm. of sodium hydroxide, COOL, and then add 20 gm. of 3,3'thiodipropionic acid.

Part C is the ferric ammonium oxalate at a concentration of 0.45M. This works out to 19.3 gm. in 100 ml. of water.

These will hold up very well if kept separate, the FAO being the least stable.

When mixed, the sensitizer should last about one half hour before the gold starts dropping out. I mixed up 10 ml. once, didm't use it all and came back the next morning to a brown bottle, the inside of which was coated with pure metallic gold.

The exposure is very similar in duration and wavelength requirements to Pt/Pd printing.

Develop in a 1% solution of either tartaric acid, citric acid, oxalic acid, or EDTA. Do not reuse.

Clear for a couple of minutes in 5% Edta and/or Kodak Hypo Clear. Papers I have used seem to clear easily.

Paper choice and developer choice will influence final print colors. The humidity of the coated paper prior to exposure greatly influences print colors. This is due to the differing sizes of the deposited gold particles. I have heard of color ranges from blacks to pinks and blues. I have made prints showing a split, with blue highlights and burgundy shadows.

Good luck, this should get you started. John Rudiak