In the process of researching or conserving old pinned insects, it’s common to find a green deposit clustered around the pin. This is known as verdigris and is a natural patina created when the metal oxidizes over time. Katherine Child is Image Technician in the Museum’s Life collections and takes photos of insects for researchers, students, artists and publications. She is also an artist in her own right, so when she witnessed verdigris being removed during a conservation project, she came up with an inspired idea.
A few years ago I read a book called Colour: Travels Through the Paintbox, by Victoria Finlay, and was interested to learn that verdigris was once used as a pigment. Verdigris, which I now know translates from French as ‘Green of Greece’, is a word that’s been in my vocabulary since I was small. I loved its rich bright blue-green colour, which is often seen on old copper piping or copper statues.
Verdigris forms when copper or a copper alloy reacts with water, oxygen, carbon dioxide or sulphur.
As early as 5thcentury AD, it was used in paint-making, and until the late 19th century it was the most vibrant green pigment available. But it was unstable – Leonardo da Vinci warned that it ‘vanishes into thin air if not varnished quickly.’ These days synthetic pigments provide a more constant alternative.
Despite its past uses, verdigris is a big problem in pinned insect collections. Nowadays stainless steel pins are used, but pins containing copper still remain in old collections and these react with air and insect fats. The more fatty the insect, the more verdigris tends to form and, if left, it can damage a specimen irreparably.
Comprising around five million or so insects, the Hope Entomological Collections here in the Museum take quite a bit of looking after. A few years ago a project to catalogue and conserve many of its butterfly and moth specimens was undertaken and the removal of verdigris and repining of insects was part of this.
With paint-making in mind, I asked that the beautiful, but problematic, substance be saved. About three years on I finally got around to using the pigment, which I had also been adding to while photographing the collections.
I chose a variety of differently shaped moths to paint (most of the verdigris came from moths, so moths seemed the most apt subject). To narrow my options further I went for green moths. Some of the specimens I chose had verdigris on their pin, so I was able to take pigment and use it to paint the very specimens from which it came!
After a first failed attempt to make watercolour paint (during which pigment and water remained stubbornly separate due to the greasy insect fats still present), I tried again, this time using linseed oil to make oil paint – and it worked! Traditionally a flat bottomed tool called a muller was used to press pigment into the water or oil. Not having one of these, I used the flat end of a pestle and a mortar which did the trick.
The paint went surprisingly far and, following on from the 14 green moths, I plan to use up the remainder to paint beetles.
Katherine’s Miscellany of Moths painting can be seen on display in the Museum’s Community Case until 18th October.