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Mr T

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Posts posted by Mr T

  1. Hm, I had a feeling that its addition might predate the current author's involvement. Might give it a shot anyway as I don't know where else I could find any information.

    I have a lot of old CCGB... it's in the 2005 (and later) edition at £450, also in the 2001 edition at £450 (pre Perkins) but it's not in a 1987 edition.

    It's not in my old Krause catalogue, or in an old Spinks or in a coin yearbook.

    But it is in Coincraft where it says "Error coin with New Zealand reverse; weight 5.8 grams; possibly unique" and a value of £500.

    Hope that helps,


    Thanks Mark, very helpful.

  2. Given that NT and AT both occur and at some point the boundary between the two must become a little blurred. How does anybody decide what is natural and what isn't? It seems to me that the opinion here is: if it's brightly coloured or multi-coloured then it must be AT, otherwise it's NT.

    Reading this it's not too clear what is accepted as natural and what isn't.

  3. coins with these appearances did not seem IMO to appear until the last 12 to 15 years

    Well that's interesting.

    I remember quite recently seeing some Morgan dollars with toning like that and the asking prices were really high for otherwise ordinary coins.

  4. Well... that depends on concentration, time scale and initial condition of the coin. The treatment with EDTA can cause an orange coloured and pitted surface.

    Surely I can bet, that you used an highly concentrated EDTA-solution, incubating for several hours a strongly corroded coin... ;)

    I am talking about a diluted EDTA-solution and a treatment of minutes, not hours or days. And the coin was not "holed" by corosion. Such a coin tends to by worthless for a collector (in terms of financial value) anyhow...

    It was a pretty badly corroded coin and I didn't dilute the stuff (some descaler) so that could have been the issue.

  5. That will be inevitable I'm afraid, where the verdigris has actually eaten away the affected surface of the coin. The only alternative is to convert the verdigris itself into another, non-corrosive substance - it may be that diluted vinegar will do that? Not sure - it will certainly lighten the rest of the coin and leave the verdigris as a dark patch, but not green.

    That depends how deep the coorosion went through the material. EDTA do not desolve the elementary metal atoms, but the charged metal ions within the green copper carbonate.

    So it shouldn't noticeably ruin the rest of the coin? I've tried cleaning some worthless coppers before but have ended up with bright orange coins with entirely pitted surfaces.

    What does the acid component of Olive Oil become once any micro-smear on the coin has reacted with the coin's surface, and thus attained a new chemical property?

    With olive oil, all sorts of things given that olive oil seems to be made up of all sorts of acids.

    If you were take the simpler example of vinegar which is acetic acid, acetic acid will react with the verdigris (copper carbonate) to give water, carbon dioxide and copper acetate. The copper acetate is soluble (dissolves in water) so if you give your coin a rinse afterwards it should be fine. I don't know if the copper acetate would affect a coin or not but you should probably rinse it off to be sure.

    If you generalise the above reaction to the acids in olive oil, the same thing should happen anyway i.e. the acid will react with the verdigris to give water, carbon dioxide and a soluble copper compound.

  6. Another good point! So, what happens chemically when olive oil goes off? Is it a danger to coins at that point? Certainly smells different when very old, so what happens?

    Also, when I talk about 'flips' in the above, I'm referring to the glued shut 2x2's with the circular plastic windows in them.

    Not sure. Maybe the acids react with air and the solution becomes non-acidic. I'm sort of guessing here.

    I believe http://en.wikipedia.org/wiki/Polyethylene_terephthalate is what the plastic in flips/2x2s and if you do a bit of quick googling you'll see that PET a.k.a polyester takes forever to break down, but acid can hasten the process.

    In order to remove plaques of corrosion a solution of EDTA proved to be quite useful. By that kind of treatment the green deposit is removed within minutes.

    Does it leave copper coins with a pitted surface?

  7. I suspect that even those "nominal bronze" plated issues will not be around much longer

    No, probably not. I'm not familiar with all of the bronze/plated issues you referred to, but the Solomon Islands as of last year no longer has any copper coins, plated or otherwise; as of 2006 Papua New Guinea no longer had its low denomination copper plated coins and Australia hasn't had any circulating bronze since 1991 (though the bronze coins were remade for mint/proof sets in 2006 and 2010).

    New Zealand has had its copper plated 10c only since 2004 or 2005 though, so it might linger for a bit yet.

    I guess copper-nickel is the new bronze.

  8. One wonders how many of todays issues will escape corrosion for future collectors.

    I've never really considered it but you make a good point. With modern day mint sets the situation could be worse I guess, but looking at some bulk bronze coins I have (most of which have at least some verdigris), it could be better.

    Also, I think Fiji, New Zealand and the Solomon Islands at least used to have bronze coins before switching to plated.