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Chemistry Notes

Gold, Platinum and Palladium Salts

For several reasons, the Gold, Platinum and Palladium salts I use in my printing pose very little danger to the environment. Gold, platinum and palladium are not “heavy metals” in terms of metals such as arsenic, cadmium, chromium, selenium, lead, or mercury. These are all nasty, dangerous poisons that chemically bond easily and tightly with other elements. These poisons can and do accumulate in your body over a long period of time. These are the nasty “dark side” chemistry I try to stay away from.   While using some of these “heavy metals” as toners, or as in the case of Potassium Dichromate I use for gum printing, I am well aware of the dangers both to myself and other animals, and of the danger to the environment by improper use or disposal.

“Noble” metals, such as platinum, gold and palladium are so-called because they are almost always found in nature in their pure metallic state. The reason is that when they form salts by combining with other chemicals, they don’t create a tight bond. A weak bond breaks down quickly when the salts enter the real world with a natural environment. What remains after a very short time are metallic platinum, palladium, gold and their respective chlorine salts. The palladium salt we use to make prints breaks down to palladium and sodium chloride (table salt). With platinum, there remains a metallic platinum and potassium chloride, commonly used as a salt substitute in low sodium diets. Gold forms auric chloride.  Neither these salts nor the noble metals themselves are any serious threat to people or the environment. Gold, platinum and palladium metals are so non-reactive you could safely eat them and they would likely pass through your body without harm. But I don’t suggest anyone test that.

Ferric Oxalate

For platinum/palladium printing, I use ferric oxalate as the light-sensitive ingredients of the sensitizer I hand coat onto the fine art papers.  Ferric oxalate is one of those weakly bound chemicals that if disposed of into the environment quickly breaks down into ferrous oxalate and then to oxalic acid and ferric (Iron) oxide, commonly known as Rust. Rust isn’t dangerous, except on highway bridges.


All of the platinum and palladium developers I use are salts of weak organic acids. Some toxic, but not anymore toxic than the many naturally occuring environmental toxins. Many of these same organic acids are commonly found in the foods we eat. Citric acid gives lemons their sour taste, and is often added to prepared packaged foods as a preservative.  Oxalic acid in dark green leafy vegetables like spinach gives them their bitter flavor. Malic acid makes some apples more tart than others. Tartaric acid gives the “tart” flavor notes to wine.  Vinegar is mostly ascetic acid and water. There’s lactic acid in milk. Formic acid causes the pain from a bee sting. Etc, etc.  If you take common baking soda, and mix it with one of these acids, it will fizz and generate foam. When the bubbling stops, the acid is neutralized and a weak organic acid salt has been formed. Use citric acid and baking soda, you get sodium citrate, a good platinum developer.

Out of this group, the oxalates are the only salts that are poisonous. While the word “poisonous” sounds ominous, that doesn’t mean they are harmful to the environment or overly hazardous to people. Ten pounds of spinach has a lethal dose of oxalic acid for an average male human being.  That said, acres of spinach as a crop are perfectly safe on a farm. In small quantities, a healthy human body deals with oxalates quite easily, as the body produces natural chelates that render them harmless.  The most common developers I use, ammonium citrate, potassium oxalate, and sodium citrate, are all quite safe for our staff myself and the environment.

Chelating Agents

Most platinum printers use a variety of different chelating compounds to dissolve the remnants of the ferric oxalate sensitizer remaining after the chemical development process. Ferric oxalate is a first cousin to ferric oxide, or common rust.  Many of the compounds I use are the same compounds used to remove rust stains from swimming pools and spas, your coffee maker, and water purifiers or conditioners, and to clean or destain your bathtub.

My most commonly used compound is EDTA tetra sodium. EDTA in low concentrations is spread agriculturally in farming  used as an aid to help plants absorb iron from the soil. EDTA I sometimes add combined with sodium sulfite in the clearing bath, though I have not found the need using the two present printing papers I use with the Santa Fe or Chimayó public water so far.  

Sulfites enhance the chelating action in the clearing stage, spreading the pores of the paper for better chemical contact. Sodium sulfite is used as an oxygen scavenger agent in water treatment plants, and to treat water being fed to steam boilers to avoid corrosion problems. Citric acid is what makes grapefruit tart to the taste.  Discarded EDTA / Citric acid clearing baths I use will be quite benign to the environment since the ferric contaminants have already been reduced to rust.

None of these chemical chelating agents we use in our lab are something I would want to drink daily, but they are not overly toxic, noxious, or dangerous to human, animal, or plant.

My Conclusions

None of the chemicals we use in our process seem to be particularly dangerous, though all chemicals should be respected in handling. So in my researched opinion, platinum and palladium printing is probably safer for myself as the printer in closest contact to them.  And safer for other people, wildlife and the environment than either the usual chemistry used for black and white or color silver-halide based photography development. I use no chlorinated hydrocarbons. The organic compounds I do use are the reasonably safe weak organic acid salts. Heavy metal tints and toners I do sometimes use, but in very low quantities and  infrequently. 

I have also researched potassium and ammonium dichromate, which are used in some quantity in gum printing.  I have decided that these chemicals are not safe to use in my rural farming environment, as I have no safe way to collect and dispose of the solutions or effluent afterwards.  So all of our gum or gum over prints will be made in another location better suited to the process.

Sources of Data I have evaluated formulating our own policy: United States Environmental Protection Agency, Dana Sullivan, Richard Sullivan, Carl Weese, Mike Ware, USDA, Chemical Manufacturer Safe Handling Data Sheets, UCLA Chemistry Department, and the practices of many other fine art printers.