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<p>[QUOTE=&quot;JMGallego, post: 2650978, member: 35622&quot;]I am a retired Research Chemist and we used silica gel with cobalt chloride for many years to dehydrate samples.&nbsp; Around the mid-1990&#039;s we found out that cobalt chloride was a cancer-causing agent and decided to exchange it. (Google it as something like silica gel cobalt chloride cancer banned Europe)</p><p><br /></p><p>Unlike in the USA, in Europe, silica gel with cobalt chloride has been banned since July 2000 and replace it with the &quot;safer&quot; orange&quot; silica gel, called Sorbead Orange® Indicating Silica Gel. The main ingredient is methyl violet, formulated to change from orange to green, or orange to colorless. Methyl violet is the lesser evil of the two, it is also toxic and potentially carcinogenic, but is &quot;safe enough to have medicinal uses&quot;.&nbsp; </p><p><br /></p><p>That gave us two options, continue using regular silica gel (without the cobalt chloride or methyl violet) or calcium chloride, which is safe and a very strong dehydrator.&nbsp; In either case, use them with a small digital relative humidity meter.&nbsp; We decided to go with the old proven, stronger dehydrator, calcium chloride.</p><p><br /></p><p>In my case, I keep my valuable copper coins, zinc coins, toned coins and my valuable silver coins in a sealed drying chamber (got it at an auction many years ago) with calcium chloride, away from my coin, as mentioned, you do not want chlorides (including sulfates or nitrates) or water in contact with your coins.&nbsp; </p><p><br /></p><p>However, I do have to monitor now and then because calcium chloride will continue to absorb humidity even when it becomes liquid and can become messy, but it never near and possibly come in contact with any of my coins.&nbsp; To avoid this, I dehydrate the calcium chloride using my oven about every six months.&nbsp; Not a big deal since silica gel has to go through a similar process, but I would never put silica gel with cobalt in my oven to dehydrate it.</p><p><br /></p><p>For my safe, I keep four large sacks of clear silica gel (approx. 2&quot;x6&quot;x2&quot;) at the bottom and an old analog humidity meter. I dehydrate them in my oven more often because I leave the door open while I &quot;playing&quot; with my coins.</p><p><br /></p><p>The bottom line, I also would recommend silica gel without any indicator to prevent your copper-based coins from being exposed to humidity (I can go into the details of why, but I already made this reply too long) and get a simple digital or analog meter to monitor the humidity.</p><p><br /></p><p>Hope this helps... and sorry for the long explanation...[/QUOTE]</p><p><br /></p>

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