To make copper acetate pigment (historically known as verdigris),  expose copper metal to acetic acid. Submerge clean, uncoated copper in a sealed glass container with distilled white vinegar for one to two weeks. Scrape the resulting vivid blue-green crust off the metal and grind it into a fine powder. 

Materials Needed

• Copper: Scrap copper pieces, sheets, or uncoated copper wire. Pre-1982 pennies also work well.

• Vinegar: Distilled white vinegar (which provides the acetic acid).

• Hydrogen Peroxide (Optional): Standard 3% over-the-counter hydrogen peroxide, used to significantly speed up the reaction.

• Container: A glass jar with a tightly fitting lid.

• Safety Gear: Nitrile or latex gloves, a P-100 mask and safety goggles.

• Tools: A palette knife or stiff blade, and a mortar and pestle.

Method 1: The Fume Method (Historical Verdigris)

This is the classic, safest method that produces the brightest pigment without handling active chemical solutions.

1. Prepare the container: Place your copper pieces or sheet at the bottom of a glass jar.

2. Add the acid: Pour a small amount of distilled vinegar into a small dish and place it inside the jar with the copper, or soak a rag in vinegar and drape it near (but not directly touching) the copper.

3. Seal and wait: Seal the jar tightly. The acetic acid fumes will react with the copper over the course of 1 to 3 weeks.

4. Collect the pigment: Remove the copper and carefully scrape the crusty, blue-green powder off the surface using your blade.

Method 2: The Submersion Method (Faster)

To speed up the reaction from weeks to days, you can submerge the copper directly.

1. Mix the solution: Fill your glass jar with a mixture of equal parts vinegar and hydrogen peroxide.

2. Submerge copper: Drop your clean copper pieces into the liquid.

3. Wait for reaction: The liquid will begin to bubble and turn cloudy before eventually shifting to a vivid, clear blue. Allow the copper to react in the solution for a few days.

4. Evaporate: Remove the copper and allow the remaining blue liquid to evaporate in the open glass container (in a well ventilated area outside, and away from pets and children.). Solid copper acetate crystals will be left behind.

Processing and Using the Pigment

1. Grind: Place your scraped crust or evaporated crystals into a mortar and pestle. Grind the material thoroughly until you have a uniform, fine-grained powder.

2. Mix into paint: Copper acetate (verdigris) is a true pigment, but it is water-soluble. It is notoriously unstable when mixed with water-based binders like gum arabic or watercolors (it may discolor or bleed), but it is always worth the experiemnt. It historically performs best when mixed with a binder like egg yolk (for tempera) or linseed oil (for oil paint).

3. To make ink, mix the clear blue liquid and the milky liquid together and add a few drops of gum arabic.

4. Safety: Copper acetate is mildly toxic if ingested. Always wear gloves during the scraping and grinding process, and do not prepare pigments on surfaces used for food.