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Best Etched Meteorites?

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#1 Kent10

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Posted 06 September 2013 - 05:55 PM

I have been looking at etched meteorites and was wondering if there is a consensus on the favorite markings or is it completely a personal thing.

For example I really like this one MUONIONALUSTA

Also, I have noticed that some MUONIONALUSTA look better than others. Is it the way the etching is done or is it just that some rocks look better than others. Or is it the lighting in these 2 examples. Thanks, Kent

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#2 Kent10

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Posted 06 September 2013 - 05:55 PM

2nd one

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#3 Kent10

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Posted 07 September 2013 - 09:28 AM

Another I like

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#4 Kent10

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Posted 07 September 2013 - 09:41 AM

I have been doing more reading and it seems many like the Gibeon (the one above) and the MUONIONALUSTA just like I do. It seems the Gibeon is more stable and less likely to rust than the MUONIONALUSTA. Is the MUONIONALUSTA a real problem? And is the Gibeon problem free or just less likely to rust? Is it the most stable iron?

Thanks.

#5 Kent10

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Posted 07 September 2013 - 09:49 AM

Info I found on etching techniques

Meteorites can be etched in many different ways, some produce lighter etches and some produce darker etches. Generally the darker an etch the less details are visible. Some etchants produce fast results within few minutes, but may burn the surface of a meteorite and cause a somewhat blurry appearance. We have etched many meteorites over the years, in our opinion a lighter but detail- rich etch is preferable over a darker one. Additionally we use a very slow etching technique which brings out much more contrast between the different shades of gray present in a Widmannstätten- pattern, however, instead of a couple of minutes this process lasts up to 1 hour. For us well worth the effort.

http://midnightsunme...uy-from-us.html

#6 Kent10

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Posted 07 September 2013 - 11:37 AM

Initially I didn't particularly like the Taza but I do now. This is my sample. The markings are quite visible in this pic but normally it is difficult to see them. The surface is very reflective. I am wondering if a coating of plastic or something was put on it. Should I be able to feel the grooves of the markings.

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#7 Glassthrower

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Posted 08 September 2013 - 09:32 AM

The two major methods of etching are - nitol and ferric chloride. Nitol is the preferred method, but it is more expensive to purchase and requires more careful handling. Because of this, some preparers will use ferric chloride, which is readily available as a circuit board etchant at places like Radio Shack. It's cheap. And it produces a distinctive etch that is darker and "bolder" than nitol.

However, ferric chloride introduces chlorine into the meteorite and the result is almost always a boatload of stability issues down the road.

BTW, who are/is "Midnight Sun Meteorites"? Just curious, because I have never heard of them until now.

#8 Kent10

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Posted 08 September 2013 - 09:39 AM

Thanks for the info, Mike. I have no idea about "Midnight Sun Meteorites". I was just searching for info on etching and that came up.

#9 lee14

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Posted 08 September 2013 - 09:45 AM

Gibeons are certainly a very stable iron, they can generally do without a corrosion inhibiting treatment. Muonionalustas have been subjected to a very different environment, and as a result are more weathered, and have absorbed a greater amount of terrestrial contaminants. While they are both fine octahedrites, there is a significant difference in hardness. Gibeons cut very well, while Muons are much tougher and frequently dull a blade after a single cut.

There are two main components that contribute to the appearance of the etched surface. The type of etchant and its strength (concentration), and the final grade of the abrasive used to finish the surface, produce great variation in the contrast. I prefer nitric acid in methanol for etching, and though some recommend ferric chloride, I decline to introduce any additional source of chlorine into a specimen. The final abrasive grade can vary from around 320 grit to a mirror polished surface. The degree of the final grinding or polishing varies from type to type of iron, I find that 320 - 400 grit is appropriate for Campos, 600 for fine octahedrites like Gibeons or Muons, and a high polish to a mirror-like surface works best for Canyon Diablos.

There are differences between specimens of the same variety as well. Heat and/or shock can seriously affect the underlying crystal structure, which will be very apparent after etching. I once cut up a fist sized Gibeon that showed a typical etch most of the way through, and then came to an area of lesser contrast and diminishing bands, and finally a golf ball sized portion that lacked any Widmanstatten pattern at all. Kind of like a self contained ataxite in an otherwise typical specimen.

You generally won't feel the lines of an etch, the surface is affected only a few molecules deep. That's why the type and angle of the lighting can have such a profound effect on the appearance. Some specimens can benefit from a more aggressive etch process though, and enough kamacite is removed to leave the brighter acid resistant taenite or other bright bands unaffected. This is common in Canyon Diablos which require a longer period in the acid solution

Lee

#10 Kent10

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Posted 08 September 2013 - 09:48 AM

This is all very interesting for me, Lee. Thanks for explaining all this.

#11 Glassthrower

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Posted 08 September 2013 - 12:37 PM

Thanks for the info, Mike. I have no idea about "Midnight Sun Meteorites". I was just searching for info on etching and that came up.


I'm glad you mentioned them, because I am always on the lookout for new dealers. This particular dealer is a mystery to me. There is no clue to their identity on their website and their domain name has privacy cloaking. Now the detective work begins in earnest. :)

#12 Glassthrower

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Posted 08 September 2013 - 12:38 PM

Thanks for the info Lee. If I ever have questions about iron prep, you are on my list of experts. :)

#13 lintonius

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Posted 08 September 2013 - 01:59 PM

I have a few etched Gibeon slices and they vary in appearance. I wonder if Lee, Mike or anyone can tell which technique was used. I have only etched a couple times and I used ferric chloride. It was easy and I got pretty good results. I wish the whole slice looked as good as the part slices, which I'll show first.
Linton

99.0g part slice...

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#14 lintonius

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Posted 08 September 2013 - 02:02 PM

136.1g part slice...

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#15 lintonius

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Posted 08 September 2013 - 02:08 PM

Now compare that with this 778.0g whole slice...
I'm thinking about re-etching this on myself, but I'd hate end up with a worse result. Perhaps I should try it on the back. :question: Any thoughts?

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#16 lee14

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Posted 08 September 2013 - 02:09 PM

Glad to be of service Kent. You ask insightful questions and your photography is superb!

Lee

#17 Kent10

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Posted 08 September 2013 - 02:14 PM

Thanks Lee. I do like photography and own some good equipment but these are pics from the advertisements when I bought them. I think the photo does make a huge difference though. Some represent the meteorite very well perhaps making a piece look better than it really is :) while others it is difficult to know what it will look like when you receive it. There was one that looked totally different when I got it. I liked it more actually. I tried to take some pics of it myself but I will need to get the tripod out sometime to really do it justice.

#18 lee14

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Posted 08 September 2013 - 02:39 PM

Lintonius; nice Gibeons slices. I can't tell from looking whether ferric chloride or nitol was used. Ferric chloride leaves a higher contrast etch, but individual stones vary in etch appearance, so only a side by side comparison would help. Gibeons tend to have a very tight surface and lack any significant amount of chlorides to begin with, so the ferric chloride method is probably safer here than with the more corrosion prone varities like Campo, Dronino, Nantan, and Muonionalusta. Still, I would personally avoid it, I have a deep seated fear of chlorine contamination.

The way ferric chloride works is a bit indirect. Through a couple of reactions, HCl (hydrochloric acid) is produced, and that is what does the actual etching. It works more rapidly than nitol and produces a darker, deeper etch. Although I've never tried it, I suspect diluting the ferric chloride solution with distilled water would slow the etching process and give you a little more control.

For a discussion of etching techniques, you may consult appendix D of 'The Cambridge Encylopedia of Meteorites' (Norton) or 'The Meteorite and Tektite Collector's Handbook', (Bagnall; Wilmann-Bell).

Lee

#19 Kent10

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Posted 08 September 2013 - 02:50 PM

I also found this interesting to read

http://www.nuggetsho...?showtopic=7933

#20 lee14

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Posted 08 September 2013 - 02:58 PM

Ah Kent, I think those Muon slices are probably from the same ebay dealer you referenced previously. I agree with you about the difficulty of imaging a reflective metallic surface, it's a real challenge to get it to actually look 'metallic' and not simply varying shades of gray. Hoping to avoid any vendor issues here I'll simply say I sell on ebay as well and try to use a range of photos that represents a specimen from it's optimal appearance to a more 'casual' average contrast shot. I've got a great camera, but getting a true metallic sheen to show well is still a crapshoot for me. This is a 132 gram Muonionalusta that I had recently.

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#21 lee14

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Posted 08 September 2013 - 03:07 PM

and the reverse...

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#22 lee14

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Posted 08 September 2013 - 03:23 PM

This is a 43 gram Canyon Diablo showing some of that metallic sheen that's so elusive to capture.

Lee

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#23 Kent10

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Posted 08 September 2013 - 03:32 PM

Those are great photos Lee and really show the etch well. Yes that 1st slice in this thread is from jlacroix1 on ebay. The 2nd one is just a picture I found somewhere online for comparison purposes. The 3rd one is a Gibeon from jlacroix1 that I ended up buying. It was not inexpensive but half the price of a Muonionalusta that I was considering. The one at the top of this thread I think was $719 but it was a thick end cut 820 grams.

#24 lee14

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Posted 08 September 2013 - 03:39 PM

Lintonius- If you want to attempt to re-etch only one face, you can protect the other side with blue painters tape. Butt the seams tightly rather than overlapping, and press the tape firmly onto the surface making sure it's securely adhered at the edges. Sand the surface with 600 grit wet/dry automotive type sandpaper, keeping all the lines straight in one orientation only. The paper fills up quickly, so keep fresh abrasive on the surface. You're trying for a uniform hazy polish. The concentration of your etchant should be such that it takes a couple of minutes for the process to complete, any quicker and it's difficult to control resulting in too dark an etch.

Lee

#25 Kent10

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Posted 08 September 2013 - 03:46 PM

Lee--I thought those pics looked familiar and I recalled that I had seen them on ebay. I found your page again and you have some very nice ones. I'll have to keep an eye out. I feel like I am reaching my limit right now though. I have bought more than I thought I would and am really caught up in this. This Canyon Diablo looks interesting with the black marks in it, different than most I think. I like it.






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