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<p>[QUOTE="otlichnik, post: 4026276, member: 109731"]BD is a pain. Here is my reaction to a possible case of BD:</p><p><br /></p><p>1) Is it BD?? Lots of people mistake different hard corrosion/reaction products - like malachite - for BD. BD is soft and powdery not hard and crystalline. In the case of the coin here it certainly does appear to be BD.</p><p><br /></p><p>2) Remove the current BD. Most should be removable with soft tools - toothpick, bamboo skewer, hard (cut-down) toothbrush or other nylon brush. Try to get all of it off. When you think it is all gone keep working it with a softer brush, q-tip, micro-fibre cloth etc. to make sure. Sometimes it is necessary to use stronger tools - steel pins, soft brass brush, etc.</p><p><br /></p><p>3) When BD is removed soak in DW (distilled water) for 24 hours. Then dry. Then bake dry in oven (not microwave!!!) at low temperature (say 200 F for 15-20 minutes) to remove all moisture.</p><p><br /></p><p>4) Leave the coin for weeks and monitor it. Do not coat the coin with anything at this stage! This will just seal in whatever is there - including remaining BD if it is not all gone. And the BD can still be there invisibly - that is why this waiting stage.</p><p><br /></p><p>5) If the BD returns repeat. Or repeat + add sodium sesquicarbonate boil. Or, if really stubborn, repeat + treat with benzotriazole (a potentially carcinogenic substance so research well and use properly!!!).</p><p><br /></p><p>Warning: Other than the returning BD, there are two bad scenarios.</p><p><br /></p><p>The first is the extensive BD under a solid-looking crust. I do have some concerns that this might apply to the coin shown in this thread. In these cases, the BD is not confined to a "pit" but is more like the lake under a frozen surface. The surface will often be flakey and break during cleaning. I have no good solution for this nightmare scenario though I would avoid any tools and stick to soaks. </p><p><br /></p><p>The second is the powdery surface - where the entire surface suffers from a BD-like decay and any treatment - sometimes even a DW soak - removes all detail leaving a slug. This is usually found on late Roman bronzes from areas where lots of fertilizer was used (Britain, France, etc.) or highly acidic soil (some "Holy-land" coins). In my experience, all that can be done with these coins is to identify them before treatment and either leave them as is, or sometimes rub them gently between thumb and finger - I know that sounds odd but this can sometimes slightly stabilize the surface a bit, though any subsequent treatment, brushing or soak will still destroy the surface.</p><p><br /></p><p>SC[/QUOTE]</p><p><br /></p>
[QUOTE="otlichnik, post: 4026276, member: 109731"]BD is a pain. Here is my reaction to a possible case of BD: 1) Is it BD?? Lots of people mistake different hard corrosion/reaction products - like malachite - for BD. BD is soft and powdery not hard and crystalline. In the case of the coin here it certainly does appear to be BD. 2) Remove the current BD. Most should be removable with soft tools - toothpick, bamboo skewer, hard (cut-down) toothbrush or other nylon brush. Try to get all of it off. When you think it is all gone keep working it with a softer brush, q-tip, micro-fibre cloth etc. to make sure. Sometimes it is necessary to use stronger tools - steel pins, soft brass brush, etc. 3) When BD is removed soak in DW (distilled water) for 24 hours. Then dry. Then bake dry in oven (not microwave!!!) at low temperature (say 200 F for 15-20 minutes) to remove all moisture. 4) Leave the coin for weeks and monitor it. Do not coat the coin with anything at this stage! This will just seal in whatever is there - including remaining BD if it is not all gone. And the BD can still be there invisibly - that is why this waiting stage. 5) If the BD returns repeat. Or repeat + add sodium sesquicarbonate boil. Or, if really stubborn, repeat + treat with benzotriazole (a potentially carcinogenic substance so research well and use properly!!!). Warning: Other than the returning BD, there are two bad scenarios. The first is the extensive BD under a solid-looking crust. I do have some concerns that this might apply to the coin shown in this thread. In these cases, the BD is not confined to a "pit" but is more like the lake under a frozen surface. The surface will often be flakey and break during cleaning. I have no good solution for this nightmare scenario though I would avoid any tools and stick to soaks. The second is the powdery surface - where the entire surface suffers from a BD-like decay and any treatment - sometimes even a DW soak - removes all detail leaving a slug. This is usually found on late Roman bronzes from areas where lots of fertilizer was used (Britain, France, etc.) or highly acidic soil (some "Holy-land" coins). In my experience, all that can be done with these coins is to identify them before treatment and either leave them as is, or sometimes rub them gently between thumb and finger - I know that sounds odd but this can sometimes slightly stabilize the surface a bit, though any subsequent treatment, brushing or soak will still destroy the surface. SC[/QUOTE]
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