Making Verdigris — The Copper Acetate Green of Medieval Painters

Verdigris (from the Old French 'vert-de-gris', green of grey) is a vivid blue-green pigment produced by corroding copper with acetic acid vapour. It is a mixture of basic copper acetates — primarily Cu(CH₃COO)₂·Cu(OH)₂ — that forms as a crusty green patina on copper surfaces exposed to vinegar fumes. Verdigris was the most vivid green pigment available to European painters from antiquity through the Renaissance, and it remained in wide use until the 19th century when synthetic alternatives replaced it.

The process was well known in ancient Greece and Rome. Pliny the Elder described it in his Natural History (77 CE), and Theophilus Presbyter gave detailed instructions in his 12th-century craftsman's manual De Diversis Artibus. The historic method is unchanged: suspend copper plates above strong vinegar in a sealed vessel. Over 2-4 weeks, the acetic acid vapour attacks the copper surface, producing a bright green crust of copper acetate. The crust is scraped off, ground, and used as a pigment.

Verdigris has one significant drawback that medieval painters discovered the hard way: in oil paint, it gradually darkens and turns brown over time due to a reaction between the copper acetate and the oil binder. This is why many medieval and early Renaissance paintings show brown or olive areas where green foliage was originally painted with verdigris in oil. In egg tempera and watercolour, verdigris is more stable. Despite its instability in oil, verdigris was so valued for its vivid, transparent green that painters continued using it for centuries.

초급

30 minutes active, 2-4 weeks passive

안내

Clean the copper sheet

Start with a piece of copper sheet approximately 10×15 cm and 0.5-1 mm thick. Clean the surface thoroughly by sanding with fine sandpaper to remove any oxide layer, then wipe with vinegar to degrease. The copper surface must be bright, bare metal — any grease, lacquer, or heavy oxide will slow the reaction. Multiple smaller pieces give faster results than one large piece because more surface area is exposed to the vapour.

이 단계의 재료:

Copper Sheet (0.5-1mm)1 개

필요한 도구:

Fine Sandpaper (220-400 grit)

Set up the vinegar chamber

Pour 200-300 ml of strong white vinegar (at least 5% acetic acid; stronger is better) into the bottom of a wide-mouth glass jar, ceramic crock, or plastic container with a lid. Create a support to suspend the copper above the vinegar without touching the liquid — a small wooden rack, crumpled wire mesh, or a shelf of wooden sticks across the jar. The copper must be exposed to the vinegar vapour, not submerged in the liquid. Seal the container with its lid.

이 단계의 재료:

White Vinegar for Cleaning300 ml

필요한 도구:

Glass Jar (500ml)

Wait 2-4 weeks for the green crust to form

Place the sealed container in a warm location (20-30°C). Warmth accelerates the reaction. Check progress every few days. Within the first week, a pale green film will appear on the copper surface. Over 2-4 weeks, this builds into a thick, crusty green layer of basic copper acetate. The crust may be bright green, blue-green, or turquoise depending on temperature and vinegar strength. Do not disturb the copper during this period — movement can dislodge the forming crystals.

Scrape off the verdigris crust

Remove the copper sheet from the jar. Scrape the green crust off carefully with a palette knife or stiff blade, collecting the powder on a clean surface. The scraped copper can be returned to the jar for another cycle — each round produces slightly less verdigris as the copper thins, but a single sheet can be reused many times. Expect 5-15 g of verdigris from a 10×15 cm sheet over one cycle. Wash hands after handling — copper acetate is mildly toxic if ingested, though not dangerous to touch.

필요한 도구:

Palette Knife

Grind and store the pigment

Grind the scraped verdigris in a mortar and pestle to a fine, uniform powder. The finished pigment is a vivid blue-green — one of the most intense greens available from any natural pigment source. Store in a sealed glass jar away from moisture. To use: mix with egg yolk for tempera (most stable), gum arabic for watercolour, or linseed oil for oil paint (note: verdigris darkens over time in oil). Verdigris is also used in manuscript illumination, where it was often glazed over gold leaf for a luminous green effect.

필요한 도구: