rust-like patches on shells

[paul monfils]

I agree with Dave. These shells have been in contact with an iron source under wet conditions. Bleach won't touch these stains.  Actually they are not exactly "stains".  As Dave observed, such iron deposits seem to eat into the shell.  More precisely, they actually become part of the shell.  A brief chemistry lesson ... metals are arranged in what is called the electromotive series, or the replacement series.  Without going into the actual molecular changes that occur, suffice it to say that a metal higher in the series will replace a metal lower in the series in a compound containing that lower metal.  The shell of course is composed largely of calcium compounds.  Calcium is very low in the replacement series, and iron is quite high in the series, so when iron comes in close contact to a calcium compound in the presence of water (especially salt water), iron atoms actually kick calcium atoms out of the compound and take their place.  The only way to effectively remove the iron would be to expose the shell to a solution of a metal higher in the series than iron.  Two problems here ... first, most of the metals higher in the series than iron are very expensive and/or very toxic (cobalt, mercury, lead, silver, platinum, gold).  And secondly, any metal that would replace iron would also rapidly replace calcium.  So there you have it - such stains are essentially permanent.

There is one approach I have used occasionally to remove a light rust stain from a non-glossy shell like a Buccinum.  Application of a weak acid solution with a cotton swab, just on the stained area, will remove such a stain if it isn't too deep.  Vinegar will work but it's a very weak acid, so it will be slow going.  However, you should be aware that what you are actually doing in this case is removing the layer of shell in which the stain resides.  The stains on these nerites look pretty deep however.  You might have a chance with the conch, but frankly it probably isn't worth the effort on such a common inexpensive shell.  <span class="petit">--Last edited by Paul Monfils on 2010-04-11 20:06:37 --</span>