Verdigris is a blue green pigment which has been used since ancient times, and is mentioned by Pliny the Elder in Roman times, and has probably been used since copper has been mined.
It is easy to make and is made as it provides a different colour to modern paints which don't use it due to its slight toxicity. It is also used to recreate the art of history.
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I make every effort to ensure the safety advice and precautions contained in this instructable are correct and that you will not be hurt if you follow my safety precautions and any other sensible precautions. However, I accept no liability or responsibility for any problems due to any errors or omissions in the content of the instructable. If you are unsure of anything please research it further and do not do anything unless you are sure it is safe.
Although if you are sensible you should not hurt yourself.
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Step 1: What Is It
It has been used thoughout history for its bright green colour and its resistance to fading when in an oils paint.
It is a mix of mainly hydrous copper(ii) acetate crystals with small amounts of other copper compounds such as, oxide, chloride, sulphide.
The modern French means green of grey but comes from the old French vert-de-Grèce "green of Greece" the English also comes from this. Many other languages call it "green of Spain" e.g. the German "grünspan".
Step 2: Necessary Substances
The easiest way to make verdigris is to react copper metal with acetic acid.
Copper is easy to get and common sources are scrap copper piping and old copper coins. If you are using old 1 and 2 pence coins it is worth using a magnet to see if they are solid copper as more recent ones have iron cores and so are magnetic.
The easiest way to get acetic acid is to use vinegar. However, vinegar is not very concentrated and even distilled white vinegar is only around 10% acetic acid. Other vinegars can be used but tend to be slower, although they can provide slightly different colours due to impurities. The picture of verdigris in the intro is a sample made with distilled vinegar.
Due to the strength of the vinegar, it takes quite a while so some people use hydrogen peroxide as a catalyst to speed up the reaction. However, as I was making a small amount, I did not bother, as it only took about a week to make a few grams. Also keeping the reaction warm (around 30* C) helped to speed up the reaction.
Step 3: Reaction
The best way to do the reaction, I think, is to seal the vinegar and copper in a container so that the vinegar cannot evaporate. Ideally use a chemically inert container such as a glass jar.
Due to the low concentration of acetic acid in vinegar it is easier to add an excess of copper which can then be removed when the reaction stops as the verdigris will be in solution. As all the vinegar will have reacted the liquid should just be verdigris dissolved in water although there will probably be a few impurities.
I left mine in a sealed glass jar for about a week before removing the excess of copper. (I used old two pence coins)
Step 4: Crystallisation
Once you remove the copper you will be left will be left with the verdigris dissolved in water. You could use it as it is as a dye however it is very dilute. I left mine on a radiator with no lid for about two days to fully evaporate.
Occasionally, especially if the mixture has been left for many days there will be cuprous oxide (CuO) present, as the copper will react with water. This can muddy the colour of the verdigris as it is a yellow to red colour. The good news is that it can be solved by adding water to the mixture as the copper oxide will not dissolve but the verdigris will and so can be separated by filtration or decanting. This cuprous oxide tends to be a yellow colour when in a very fine powder, but if the crystals are larger it will appear more red. Once separated from the verdigris it can be used as a pigment in its own right or can be used for its anti-fungal properties.
As the crystals I was left with were rather small I put them in a small glass bottle as they were. For use as a pigment you would want to grind them into a powder but I prefer to keep it as small crystals as it is less messy if I spill it. The crystals are easy to grind into a powder which is a lighter blue than the crystals.
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