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!

 

[copper123]

Looks like a real winner now , I would try it sometime with a suitable coin I am sure you have at least doubled the coins value , its not worth a fortune but there again who wants to experiment with really valueable coins.

[copper123]

Heres my 1799 a lovely example bought recently at least EF with lustre and no problems only £20 I wish i had a 1806 and 1807 is similar grade

[david.bordeaux]

Another trial.

[Paddy]

Ah now that shows great promise!

 

[Coinery]

Brilliant result! 

[Peckris 2]

On 2/19/2026 at 5:47 PM, copper123 said:

Heres my 1799 a lovely example bought recently at least EF with lustre and no problems only £20 I wish i had a 1806 and 1807 is similar grade

 

Strangely, the 1806 is so so common in lower grades but much scarcer than the penny and farthing in top grades.

[copper123]

21 hours ago, david.bordeaux said:

Another trial.

while there's still a nasty spots there it is at least a bit more collectable and the horrid green colour has gone - nice one  

[SilverAge3]

Have you heard of using gun bore cleaner? Not sure how accessible that is over there. I know it is part of the process used by a guy over here, for cleaning copper, bronze. But the rest he keeps pretty secret.

Edited Saturday at 10:11 PM by SilverAge3

[SilverAge3]

In other words, roll the swab between fingers/thumb, don't wipe or rub.

 

Use the technique in this video

 

 

Edited Saturday at 11:06 PM by SilverAge3

[david.bordeaux]

This experiment was with 5% sesquicarbonate at room temperature for 6 hours. The green spots have gone but the coin looks stripped and cleaned. I'm going to try 2% at room temperature with a shorter contact time.

 

 

[Paddy]

1 hour ago, david.bordeaux said:

This experiment was with 5% sesquicarbonate at room temperature for 6 hours. The green spots have gone but the coin looks stripped and cleaned. I'm going to try 2% at room temperature with a shorter contact time.

 

 

Incidentally, when you did your initial experiment - 100 minutes at 90C - how did you achieve this temperature control?

[david.bordeaux]

4 minutes ago, Paddy said:

Incidentally, when you did your initial experiment - 100 minutes at 90C - how did you achieve this temperature control?

Using a bain-marie and a thermometer. The temperature fluctuated between 85 and 95°C.