Experiments with verdigris treatment

[david.bordeaux]

I don’t like using proprietary products because I don’t know what’s in them, and I believe VerdiCare is difficult to obtain in the UK anyway. After some research on what the British Museum used to use to treat bronze disease and verdigris on large objects, like cannon, I tried the technique for myself on this battered 1799 half-penny.

 

For anyone interested, the treatment was 100 minutes at 90°C in a 2% w/w solution of sodium sesquicarbonate in chlorine-free water. Followed by a rinse in chlorine-free water to remove the chemical and then a rinse in acetone to remove the water. The heat is needed as the reaction is impossibly slow at room temperature.

[Peckris 2]

Three questions:

1. where do you get sodium sesquicarbonate from?

2. Presumably filtered water (Brita) counts as chlorine-free?

3. dabbing with a soft towel would do instead of acetone to remove water?

[david.bordeaux]

Just now, Peckris 2 said:

Three questions:

1. where do you get sodium sesquicarbonate from?

2. Presumably filtered water (Brita) counts as chlorine-free?

3. dabbing with a soft towel would do instead of acetone to remove water?

1. I bought mine on Amazon. It is also available on eBay and from pet shops (for use as a buffer in fish tanks). It is sometimes branded as "Borax substitute" or "Crex" but read the label carefully - it must be sesquicarbonate.

2. Yes, Brita filters remove chlorine.

3. Yes, but not so effective as a quick dip in acetone.

[Paddy]

I can see that the treatment has lightened the tone quite a bit, but I don't see any real verdigris, before or after. Have you tried it on obvious verdigris?

 

[Peckris 2]

13 minutes ago, Paddy said:

I can see that the treatment has lightened the tone quite a bit, but I don't see any real verdigris, before or after. Have you tried it on obvious verdigris?

 

Strange. To my eyes the treated coin is DARKER.

[david.bordeaux]

5 minutes ago, Paddy said:

I can see that the treatment has lightened the tone quite a bit, but I don't see any real verdigris, before or after. Have you tried it on obvious verdigris?

 

The verdigris may not show very well in the photo. Below is another "before" photo under different light.

Work is in progress on coins with more obvious/stubborn verdigris. I will report back!