Verdigris problem

[sanjuro]

Serious question:

I have a handachi style fuchi kashira set in shakudo, part of a full koshirae. The kashira/kabuto gane is infected with green verdigris (see Pic). I wish to neutralise or better still, remove this. As I see it I have a couple of alternatives. Since the verdigris will only form on the base copper, then obviously the shakudo patina is thin or otherwise compromised in the affected area. Removing the verdigris by abrasion will obviously damage the surrounding patina. I dont want to do this.

Question: what can I use to neutralise the verdigris and mask the colour of it? It seems to be slightly granular in nature so possibly it may lift if treated with a chemical or oxidant of some kind. What can be used safely?

 

[ROKUJURO]

Keith,

 

if there is an expert to answer this competently, it is Ford Hallam!

[Alex A]

Hi Keith, i too would be concerned about what chemicals to use, theres plenty on the net about removing verdigris from copper coins etc, maybe theres a coin collector on here who knows if it can be removed without damage and give you the safest method...

 

Alex

[Brian]

Shakudo is mainly copper, with about 3% gold. So no way it is covered with thin shakudo. It is either solid shakudo or not. Are you sure it is shakudo and not just patinated copper etc?

Habaki are sometimes shakudo covered, but not f/k to the best of my knowledge.

Obviously, to prove me a liar, there will be exceptions out there :D

 

Brian

[sanjuro]

Brian

 

I understand what shakudo is. Maybe its the way I put it but it is solid shakudo alloy. The patination however comes from a pickling solution, and its this patina that I dont want to destroy. Sorry If I made it sound as though the piece was covered in shakudo.

 

Fuchi Kashira set, in shakudo. Not 'set in shakudo'. This is where I think I led you astray. Or possibly when I referred to the shakudo being thin. The patina is what I should have referred to as being thin. My Bad.

[Ford Hallam]

Hi Keith

 

Verdigris is in essence a form of rust on copper or cuprous alloys. It's a complex mix of various naturally occurring copper salts, (acetate, chloride and carbonates). It can't really be stabilised other then by keeping the piece in as stable and neutral environment as possible. Because verdigris is hygroscopic (it attracts moisture) it will keep reacting as long as there's moisture in the air.

 

There is a specialised chemical solution used by museum conservators that can dissolve and break down verdigris. I've used it very successfully on bronzes and the underlying metal was conveniently left deep brown, much to my clients delight. Unfortunately I doubt it would result in the same happy result on shakudo. Any chemical solution that will remove the verdigris will also eliminate the patina.

 

You can try rubbing at it with a wet toothpick to eliminate as much as possible. Then washing well with a mild soap, green Fairy Liquid is perfectly fine. Dry well, warm with a hair dryer until quite hot to the touch and seal with Renaissance wax.

 

If I were to deal with it I'd completely remove all trace of the corrosion using the appropriate acids, refinish the damaged areas as much as is feasible and then re-develop the patina to blend with the original colour. This is not a job for an amateur nor someone inexperienced in these processes. I merely describe the approach a professional would take and hasten to add I know of no other professionals experienced in these processes as they relate to traditional Japanese metalwork.

 

And just to correct a common misapprehension. The patina is developed in a very mild copper salt, (ironically in this case, a variety of verdigris and copper sulphate) neutral aqueous solution. When we use the word 'pickle' it refers to an acid solution intended to remove oxides and flux resides resulting from soldering.

 

regards,

 

Ford

[runagmc]

Ford, just for my own interest, why would you not remove the patina completely on both fuchi and kashira and repatinate everything? I assume it's because you want the pieces to remain in their original state as much as possible... Or would doing it that way just be more work?

[Ford Hallam]

Adam,

 

completely stripping both pieces and repatinating them would be the easiest approach for me but in principle it is sometimes worth preserving what we can, if it's in reasonably condition.

[sanjuro]

Ford and Adam.

 

Firstly I would like to thank Ford for his interest and his suggestion of how to tackle the problem.

What Ford has said above resonates well with my own thoughts regarding this particular set of FK, particularly since there is an element of wear and age to the patina that I want to preserve if at all possible, and which would be difficult to reproduce if the whole set was completely repatinated. Since 90% or more of the patina is intact, It would be a pity to lose that for the sake of this small area. Having said that, I dont doubt that Ford could reproduce the original patina perfectly and even make it look aged and worn if required, but it would be extra work to distress or fade the patina with wear that has been centuries in the making, and original in this case is better if it can be preserved.

So this is how I have approached it thus far........ The wet toothpick method yielded minimal (if any) result after an hour of rubbing, so I modified Ford's method a little.

Since verdigris is hydroscopic, I cleaned down the area with methylated spirit to dry out any of the water that may remain in the verdigris. I then used a small horn spatula that I have used in the past for cruddy menuki, to wear away and scrape gently at the verdigris. This worked without touching any of the original patina. The verdigris comes off as a greenish white powder. (some of the spatula is also worn away in the process). Repeated wiping with the methylated spirit on a cotton bud removes the residue. Thus I proceeded until no more residue was coming away from the surface. The patina is still intact. I shall have a further session doing this and when sealed with wax as per the original method I'll post a pic to show the results.

Now Ford can berate me with criticism for altering his suggested method, but the results so far are most promising and I have not violated the first commandment, "DO NO HARM".

NB. Should it come to pass that I screw it up completely, I'll give it to Ford to repatinate, and he can gloat appropriately. :D

[Ford Hallam]

Keith

 

no gloating from me :D The approach you took is absolutely correct. Start with something relatively soft and move on to something slightly more hard if required. I look forward to seeing the results. Sounds as though you've on track through.

 

cheers,

 

fh