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
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
Michael Gilmer - Member of the Meteoritical Society & Collector of Falling Stars.
☄ ⒼⒶⓁⒶⒸⓉⒾⒸ ⓈⓉⓄⓃⒺ - www.galactic-stone.com
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!