Varnishing

[Taikonaut]

I see this fairly frequently with ancient bronze coins althogh it happens in other periods too.

Why does people varnish coins? 

 

[jelida]

Varnishing was thought to be protective of a coin by excluding moisture, air and reducing the impact of handling, I can remember in the ‘70’s Lindner sold kits of three wide neck jars of , I think, cleaner, varnish and varnish remover;  it was meant to be a reversible process, if you used the right materials. Personally I don’t too much mind it on ancient, patinated bronze, but it seems pretty pointless on unpatinated copper alloy and silver or gold.

Jerry

[JLS]

12 hours ago, Taikonaut said:

I see this fairly frequently with ancient bronze coins althogh it happens in other periods too.

Why does people varnish coins? 

 

Are we talking about using actual resin-based varnish, or lacquering ? 

The first is not a great idea, people still commonly lacquer pre-1600 copper - I've done it myself. 

[jelida]

Certainly shellac, which despite being soluble in meths etc eventually forms an irreversible bond and reacts with copper corrosion products and is not a good idea, nor I suspect polyurethane varnishes which require specialist solvents and can be a bu**er to remove. Really the difference between lacquer and varnish is one of terminology, the key thing is that it must be removable , thinly applied and not attract dust etc or it should not be used, and even then I feel for patinated copper alloy only. I do admit to using Incralac on my better ‘dug’ Roman Bronze coins, an archival lacquer soluble in acetone but which contains Toluene, and Benzotriazole to inhibit bronze disease, so itself carries a potential carcinogen label and must be treated with respect.
Jerry

[Taikonaut]

I hated the varnish. I use alcohol and got rid of it and the coins look better. I think the only argument in favour is protection from handling. Does museums use Ren Wax on ancient coins?

[JLS]

On 1/26/2020 at 4:52 AM, Taikonaut said:

I hated the varnish. I use alcohol and got rid of it and the coins look better. I think the only argument in favour is protection from handling. Does museums use Ren Wax on ancient coins?

The British Museum doesn't presently use Ren Wax on ancient coins. However, a lot of the collection has been lacquered by someone or other at some point. 

I think the real problem with lacquering is that in order to remove the lacquer you need to know the chemistry. And even if you sell or otherwise pass on a coin with a ticket saying that it was lacquered with mineral/organic oil or some other formulation, probably it will get lost before the lacquer looks a bit ugly. 

Ren. Wax is easy to remove because you can just boil the coin in water. 

[jelida]

3 hours ago, JLS said:

Ren. Wax is easy to remove because you can just boil the coin in water. 

I’m not sure this is a great advertisement for Renaissance Wax,  I can imagine a lot of crumbling patina with the metal expansion/contraction as it is heated/cooled.

I agree regarding the lacquer , inappropriate varnishes, lacquers and oils are very difficult or impossible to remove.

Jerry

[JLS]

13 hours ago, jelida said:

I’m not sure this is a great advertisement for Renaissance Wax,  I can imagine a lot of crumbling patina with the metal expansion/contraction as it is heated/cooled.

I agree regarding the lacquer , inappropriate varnishes, lacquers and oils are very difficult or impossible to remove.

Jerry

Well, it depends on the sorts of coins you lacquer. I wouldn't lacquer a coin with a very poor surface or extensive corrosion. The ideal coin to lacquer is one which has been cleaned or polished and therefore has no natural patina. 

Example from my collection attached - I didn't do the lacquering but I'm pretty sure it would be a lot uglier without. Notice the pink highlights and the unnaturally smooth/shiny look. Before lacquering most likely a problem coin, afterwards...well I don't mind the look of it.