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Sunday, June 5, 2016

Meteorite Display Cases

My wife loves meteorites, so I decided to surprise her last Christmas with a few pallasites. Pallasite meteorites have nickle-iron matrix surrounding olivine crystals of peridot. If you get thin sliced specimens, they can even be see-through. Very pretty. Unfortunately, they have a bad reputation of rusting and falling apart if not cared for properly. With that in mind, I attempted to create a display case for them. I do not recommend using the method described for my first attempt.

Finished product first. Attempt 1
I purchased a cheap display case of off amazon, and lined the opening with foam rubber to help it seal better. A piece of thin plastic was placed on top of the included foam covering a few magnets that would help hold the meteorites in place. Labels were created for each one. The square and rectangle in the top right are a de-oxygenator and silica packet respectively. I make my own silica packets using coffee filters, a stapler, and color changing silica beads. I bought the bulk silica beads and oxygen absorbers off of amazon; both were fairly inexpensive. Each specimen was cleaned with 99% IPA and then coated in 2 coats of CRC 3-36 Multi-Purpose Lubricant and Corrosion Inhibitor. This was recommended by a few posts I saw concerning meteorite preservation. 

This seemed to work well for about 3-4 months. Unfortunately, the case was not a perfect seal, and I think oxygen and water moisture worked their way in and saturated the oxygen remover and silica. While the Imilac, Seymchan, and Fukang meteorites didn't appear to be affected, the Brenham rusted a lot and a few spots appeared on the iron of the Brahin. 

I started researching iron meteorite care more. It seems there are a few different modes of thought. Some people offer a mysterious "stabilization" service which claims to remove all rust and prevent further rusting forever even if the specimen is left in open air. Unless this is some sort of electroplating, I can't think of any way that could really be a permanent solution. It is also an expensive procedure. Other options include: encasing the meteorite in a plastic resin or wax, leaving the meteorite submersed in oil (such as clear mineral oil) or automatic transmission fluid, and various rust inhibitor coatings like the CRC 3-36 I tried earlier. I disregarded the encasement idea because it seems to difficult to do well. Submersion in oil would probably work for long term storage, but wouldn't work well for display purposes. The oil will also seep into all of the cracks of the meteorites, which seems like it might be a bad thing. After the failure of the CRC 3-36, I don't really trust rust inhibitors for long term use. Then I came across a method which uses a desiccator jar for long term storage of meteorites. Desiccators are sealed vessels that use silica or other desiccants to drop the humidity to < 10%. I figured coupling that with some oxygen absorbers would guarantee the meteorites to stay rust free, even without a coating. While a jar will obscure the meteorite somewhat, precluding using one for display, clear acrylic and polycarbonate desiccator cabinets exist. I picked one up in good condition off of eBay for $130. 

For the second attempt, I cleaned the meteorites as best I could using IPA, q-tips, and paper towels. The CRC 3-36 coating is difficult to remove fully, and left a haze on some parts of the meteorites. I  do not recommend using this spray for meteorite preservation. Unfortunately, the Brenham specimen crumbled. Rust was visible on all crystal-iron boundaries. I scrapped the fragments into a small ziplock bag and placed a silica packet in it. I placed the largest chunk and the other meteorites on a baking sheet and baked them for 1 hour at 200 F. That should cause all of the moisture present in them to evaporate. I made an extra large silica packed and placed it and two of the oxygen absorbers in the case. Here's a picture of the finished 2nd attempt.

2nd Display Case Attempt
If this seems to work well at preventing rust, I plan on laser cutting a shelf with better provisions for holding the specimens (currently, the magnets holding them are just taped to the bottom shelf). I may also add LED back-lights with a magnetic switch so I don't have to cut into the case. All of the specimens have some transparency, so the back-lights would make a nice addition.

In summary, don't trust rust inhibitor coatings or imperfectly sealed display cases to keep your iron or stony-iron meteorites rust free. While I can't speak to the effectiveness of oil submersion or the "stabilization" procedures, I will report the results of my desiccator cabinet experiment in a few months.


UPDATE:
It's been a few weeks. The silica is still blue, meaning the case's seal is good and no moisture is leaking in. No signs of further rusting/damage. I need to spend some more time trying to remove the old corrosion and 3-36 coating; the meteorites have some clearish-white smudges on them from when I tried to remove it before. Overall, I think this is probably the best way to store and display them long term. Future work: create a back-lit display shelf.