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lintonius
sage


Reged: 12/13/05

Loc: south-central Utah
Re: Best Etched Meteorites? new [Re: lee14]
      #6070359 - 09/08/13 10:19 PM

Quote:

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




Thank you, Lee. Former Michael Casper pieces.
Interesting info too, though I should do some more homework before making any decisions.
I should start by pulling out Norton's CEofM.
Linton


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lintonius
sage


Reged: 12/13/05

Loc: south-central Utah
Re: Best Etched Meteorites? new [Re: lee14]
      #6070381 - 09/08/13 10:34 PM

Quote:

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




Yeah Lee. I might try the back first, so I don't lose the etch I already have. I used a random-orbital sander on prior etchings (long-time woodworker;^). I take it you don't recommend that?
Linton


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lee14
super member


Reged: 12/19/09

Re: Best Etched Meteorites? [Re: lintonius]
      #6071310 - 09/09/13 01:15 PM

I've actually considered a random-orbital sander (long time woodworker as well), but never actually tried it. I suspect that even the very fine swirls it leaves might be visible in the final etch. I suggested sanding in one direction because the alignment of the crystal plates, especially with fine and medium octahedrites, helps to disguise the visibility of the sanding marks. I finish my pieces first on a stationary belt sander to produce a flat surface, through the sequence of grits, and do the final sanding with a cloth wheel and 'dry' abrasives. Two reasons for this; grit for grit the wheel abrasives do a finer job and leave less distinct lines, and, the cloth wheel will compensate for any surface irregularities and yield a more uniform finish. Of course the foam plate on a random orbital sander might do that as well. I would certainly be interested to hear what kind of results you get.

I got my first large Campos from Michael Casper, a great person to do business with, and a fascinating individual in person.

Lee


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Kent10
scholastic sledgehammer
*****

Reged: 05/08/12

Re: Best Etched Meteorites? new [Re: lee14]
      #6079737 - 09/14/13 01:58 AM

Hi Lee:
Does your method of etching give the etch more of a matte look rather than a shiny look. Or is that the difference in types of irons. I really like the look of your Campo del Cielos which don't reflect so much light. Both the Gibeon and Taza etchings I have are quite reflective as if there is a protective coat of something on there. I don't like these as much.


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lee14
super member


Reged: 12/19/09

Re: Best Etched Meteorites? new [Re: Kent10]
      #6080695 - 09/14/13 04:15 PM

As to any difference between nitol and ferric chloride, I can't say, I've never tried the latter. There may be minor differences between types, but I suspect how the surface is finished prior to etching is more a factor for determining reflectivity. Most of mine are finely ground to 600 grit, so the surface has a matte appearance even before etching. I used to polish everything to a mirror finish, but found it generally unnecessary. The contrast seemed better without polishing, so I left out that step since it's a pretty lengthy process anyway.

Not to say you can't get good results etching a mirrored surface. Since the acid dissolves only the kamacite and leaves the taenite unaffected, that portion ought to remain quite reflective. Some species require a fully polished surface to show a good etch, such as Canyon Diablo and Mundrabilla. Etching these after only a 600 grit finish leaves a muted pattern with poor contrast in my experience.

Some folks do coat their pieces with lacquer or polyurethane. Those should appear uniformly shiney regardless of the viewing angle. Close inspection should reveal if you've got a coated piece. If there is a sprayed on coating, you will be able to slightly dent it with a gently applied fingernail without causing any damage.

Lee


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Kent10
scholastic sledgehammer
*****

Reged: 05/08/12

Re: Best Etched Meteorites? new [Re: lee14]
      #6080700 - 09/14/13 04:18 PM

Thanks Lee. Your etching is really beautiful and I can't stop looking at that piece.

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Kent10
scholastic sledgehammer
*****

Reged: 05/08/12

Re: Best Etched Meteorites? new [Re: Kent10]
      #6081901 - 09/15/13 11:37 AM

I contacted the seller of my Taza and he said there is a clear coating on it. He says he also coats all his irons with Def clear coat. I sure would like to see my Taza without the coating. I guess it must protect it but it is so reflective I don't think it looks as good as it might.

I wonder if Def is a brand or type of clear coat.


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Kent10
scholastic sledgehammer
*****

Reged: 05/08/12

Re: Best Etched Meteorites? new [Re: Kent10]
      #6082409 - 09/15/13 04:51 PM

I also contacted the seller of my Gibeon and he also coats his irons. "We use a protective coating to protect our meteorites from corrosion. It is a meteorite top coat developed and sold by a company called paleo bond." It is not as reflective as my Taza though. The Taza looks "plasticy."

I just received a 2nd e-mail from the Gibeon seller. "Yes that one had a protective coating put on it called vpci 286 meteorite top coat."


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Kent10
scholastic sledgehammer
*****

Reged: 05/08/12

Re: Best Etched Meteorites? new [Re: Kent10]
      #6082464 - 09/15/13 05:19 PM Attachment (9 downloads)

I can't believe I just got myself another Taza. I am just disappointed with the plastic one that I have and it is hard to look at. I found this one and immediately liked it. I hope it is not coated the same. Pictures look great I think and it has an inclusion!

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lee14
super member


Reged: 12/19/09

Re: Best Etched Meteorites? new [Re: Kent10]
      #6083028 - 09/15/13 11:22 PM

I like the Tazas, I think I'll have to keep an eye out for a whole one.

I'm a bit familiar with Paleo Bond through their literature, but have no direct experience with the products. I believe they're highly thought of though.

I came to use gun oil as a protectant after reading an article by Allen Langheinrich (Lang's Fossils and Meteorites) on the care and preparation of irons. It appears in the August 1997 issue of Meteorite!, which I'm pretty sure is out of print.

The use of a clear coating is nice because it enables frequent handling of a specimen. I'm not sure how they hold up over time, I'd certainly be glad to hear from anyone who's had a similarly prepared slice for a number of years. I did at one time coat my pieces, but found even the tiniest bit of trapped moisture became problematic over time, compromising the coating and accelerating corrosion at that point. I like gun oil because it penetrates into any microscopic fissures, and is easily reapplied if necessary. I have quite a few pieces treated with G-96 oil, slices and whole specimens that have remained corrosion free for years, and that is in a fairly humid environment.

Lee

Edited by lee14 (09/15/13 11:24 PM)


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lee14
super member


Reged: 12/19/09

Re: Best Etched Meteorites? new [Re: lee14]
      #6083033 - 09/15/13 11:27 PM

I believe def clear coat is simply automotive lacquer without pigment.

Lee


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Kent10
scholastic sledgehammer
*****

Reged: 05/08/12

Re: Best Etched Meteorites? new [Re: lee14]
      #6083034 - 09/15/13 11:28 PM

Yes an advantage of these coatings is that it will protect nicely but if it compromises the look... In my 1st Taza I can actually see scratch marks made in the coating and it is so reflective. I don't mind the Gibeon one. It still looks quite nice but I would sure like to see it without the coating. I also like the gun oil method Perhaps when my irons start rusting or looking not so good I will have wished I had them all coated

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lee14
super member


Reged: 12/19/09

Re: Best Etched Meteorites? new [Re: Kent10]
      #6083488 - 09/16/13 09:22 AM

That Taza certainly has a lot going on. The inclusion is either troilite or graphite, can't be sure from a pic. The underlying Widmanstatten pattern is quite muted, but attractive. Those needle-like forms are really spectacular, and probably schreibersite, Mike would probably have a better estimation. Then there are a couple of more amorphous metallic formations at 5 o'clock from the troilite. These look just like those one often sees in Canyon Diablos. I'd say this material underwent some serious shocking.

Lee


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Kent10
scholastic sledgehammer
*****

Reged: 05/08/12

Re: Best Etched Meteorites? new [Re: lee14]
      #6083496 - 09/16/13 09:25 AM Attachment (7 downloads)

I like it and I hope it looks as good in person. Here is the reverse side and a close up of the inclusion.

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Kent10
scholastic sledgehammer
*****

Reged: 05/08/12

Re: Best Etched Meteorites? new [Re: Kent10]
      #6083497 - 09/16/13 09:26 AM Attachment (14 downloads)

Close up

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Kent10
scholastic sledgehammer
*****

Reged: 05/08/12

Re: Best Etched Meteorites? new [Re: Kent10]
      #6083499 - 09/16/13 09:27 AM Attachment (6 downloads)

Other side close up

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lee14
super member


Reged: 12/19/09

Re: Best Etched Meteorites? new [Re: Kent10]
      #6083915 - 09/16/13 01:00 PM

I'm going to say troilite rather than graphite. It has the brownish tinge characteristic of troilite (iron sulfide) rather than the grayer look of graphite. What I especially like about this one is the metal crystals arranged around the perimeter. Really nice!

Lee


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Glassthrower
Vendor - Galactic Stone & Ironworks
*****

Reged: 04/07/05

Loc: Oort Cloud 9
Re: Best Etched Meteorites? new [Re: lee14]
      #6084347 - 09/16/13 05:13 PM

That is an awesome Taza. The inclusion is surely graphite, but it appears to have a ring of schriebersite around it. I'm not familiar with the chemical makeup of Taza in particular, but when one sees graphite inclusions like this in an iron meteorite, there is often a ring of schriebersite around them.

Let me preface my next statement - I am not skilled with iron meteorites and I am not particularly knowledgeable about them because I don't collect them and rarely sell them. It's not a knock on irons, it's a restraint I put on myself because the high expense and learning curve of prepping and curating irons.

Also, I live in Florida, which presents a constant battle with humidity to keep my specimens from degrading while in my possession. Plus, as Lee will attest to, irons are rough on the saw, blades, and equipment. But, I have picked up some knowledge of curating iron meteorites from Pat Mulvany. Some of his knowledge rubbed off on me via osmosis over the years. I do know that coatings are generally harmful to most meteorites - in terms of contamination and loss of scientific study value. However, many irons desperately need to be saved from oxidation, so using chemical or oil treatments and coatings is a necessary evil with irons. The only big exception to this is uncut irons that have a stable, protective shale rind around the unoxidized core. Those can last almost indefinitely in a stable state if they are properly stored and handled.

Best regards,

MikeG


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lee14
super member


Reged: 12/19/09

Re: Best Etched Meteorites? new [Re: Glassthrower]
      #6084475 - 09/16/13 06:26 PM

Is it the ring of schriebersite that leads you to the conclusion that the inclusion is graphite? I've never worked with a Taza, but the only place I've seen graphite inclusions are Canyon Diablos. The only non-intrusive test I know to differentiate between the two is that troilite tends to stain the surface if one is slow to halt the etching process. If you've got a visual method of telling whether an inclusion is graphite or troilite, please fill me in!

Lee


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Glassthrower
Vendor - Galactic Stone & Ironworks
*****

Reged: 04/07/05

Loc: Oort Cloud 9
Re: Best Etched Meteorites? new [Re: lee14]
      #6088641 - 09/18/13 06:51 PM

Quote:


Is it the ring of schriebersite that leads you to the conclusion that the inclusion is graphite? I've never worked with a Taza, but the only place I've seen graphite inclusions are Canyon Diablos. The only non-intrusive test I know to differentiate between the two is that troilite tends to stain the surface if one is slow to halt the etching process. If you've got a visual method of telling whether an inclusion is graphite or troilite, please fill me in!





No, the ring of schriebersite is just coincidental - you see similar rings around various inclusions, clasts, or even around armored chondrules in some stony types.

I am guessing this is schriebersite, but I am not sure. The schriebersite would be the innermost ring around the inclusion, and the lamellae radiating outward from it are probably the usual taenite or kamacite.

As for the inclusion, graphite is my guess, but I am not 100% certain - I probably sounded more certain at first, but after studying the photos more closely in Photoshop, I am not sure now - it could be graphite or troilite. I am still leaning towards graphite because of the color and apparent texture in the photo. The majority of easily-identifiable troilite I have seen has a brassy hue to it. But, troilite doesn't have to be brassy - it can appear greyish or it can have the same hue/color as the other metal in a given meteorite.

In general, most graphite inclusions are a bit darker in appearance than this one. And, as far as I know, graphite is not common in Taza (NWA 859). So I could be very wrong on this. A hardness test on the inclusion might narrow down the possibilities - graphite is softer than troilite, unless it is so highly shocked that the graphite has become hardened.

I would try scratching the surface of the inclusion and find out what the hardness is. Graphite is 1.5 on the MOHS scale, so you should be able to scratch it with your fingernail. If you can't scratch it easily, then it's likely not graphite - unless it is highly shocked.

Best regards,

MikeG


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