Silver Searcher said:
Great Roman Coin
I never get sick of finding them, trouble is it's not often you get them as good as yours
this one was my favourite
but it had Bronze desease and quickly fell apart
SS
Nice coin SilverSearcher...Bronze disease or cancer: the presence of chloride salts, and paratacamita atacamite on the surface of currencies consisting of copper alloys is very destructive. Cuprous chloride and cupric chloride causing spots of pale green to blue-green, soft and powdery on the surface of a coin, because they produce hydrochloric acid (copper chloride combined with oxygen and water from the air) that corrodes the currency cuprous chloride producing more ... etc. to get rid of the coin. In dry climates the problem is more strange because the reaction requires a relative humidity of 39% or more to become active.
It is easy to remove with a brush, but will appear again in a few weeks.
Mild cases.
Heat:
The heat neutralizes bronze disease temporarily removing the water needed for the reaction. This reaction will reduce your progress or stops temporarily
Put in oven at 200-250 degrees for 30 minutes to an hour. This failure to achieve a cure, the humidity can initiate the reaction again as soon as the currency to cool. In the best case, the application of heat to a currency temporarily stop or slow disease progression.
Heat can change the color of the patina, after treatment with heat, heated coins tend to be darker.
Distilled water:
The use of distilled water may seem counterintuitive since the humidity is necessary to start the reaction.
Do not use tap water. The minerals and salts in tap water could increase the bronze disease.
The most effective cure appears to be a three-step process:
1) brushed to remove as much growth as possible damage dusty surface of the coin.
2) Leave the currency dipped in distilled water, changing at least every day for two weeks to a month. This serves to remove the chlorides. These go into the water slowly (attract the chloride ions). It is essential to the processing time and frequent changes of water every few days to a week
3) After heating the oven the coins in a normal kitchen oven at 250 º C for two to three hours to remove the currency of any moisture present.
At the end of this process, if all went well, bronze disease (dusty green) will be gone. Coins can be darkened slightly due to oxidation baking. If necessary, the currency can be polished lightly with a soft cloth.
