John and Dialists, You and other folk are probably correct, I was just indicating that the surface chemistry of the worked stone may be different that in unworked areas and that this may be part of the cause of differential erosion by blowing sand. Yes, the reference I quoted from was for igneous rocks, not sedimentary.
Another interesting ( at least to me ) idea is in the area of cast stone. I don't mean various attempts to mimic stone, but actual stone. In a controversial book by Joseph Davidovits titled "the pyramids, an enigma solved" he states that ancient Egyptian technology knew how to actually cast many of the real stones, not concrete or plaster. He gives the recipies for a couple and indicates that he has patented and sells some of the formulae and casting materials for a number of others. If this actually works ( and trying a couple of his formulae, it seemed to work ) we might be able to cast stone in forms identical to natural ones, only already shaped as we wish for Sundial purposes. Such cast stone might well be better made for the purposes of lasting through years of exposure. Has anyone else explored this area? Edley McKnight From: "John Carmichael" <[EMAIL PROTECTED]> To: <[email protected]> Subject: Re: Eroded rock Date sent: Wed, 30 Oct 2002 07:28:57 -0700 Send reply to: [email protected] Sandstone dust has a very salty taste. Does that mean I should dip my stone blanks in acid before I engrave them to protect them from further erosion? A scary thought! When stone masons lay flagstone flooring, they often clean the unwanted calcium carbonate deposits off the stone using dilute sulfuric acid and a scrub brush. But I have always been afraid to use H2SO4 on my stones, fearing that it might damage the stone internally or cause the sedimentary stone layers to separate. I worry that this possible damage might take years to show itself. (But I observed no immediate damage to the stone when I experimented with H2SO4, and it did do a very good job of cleaning the stone.) So you also have to be a chemist to make sundials, huh? John John L. Carmichael Jr. Sundial Sculptures 925 E. Foothills Dr. Tucson Arizona 85718 USA Tel: 520-696-1709 Email: [EMAIL PROTECTED] Website: <http://www.sundialsculptures.com> ----- Original Message ----- From: "Edley McKnight" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Tuesday, October 29, 2002 5:34 PM Subject: Re: Eroded rock > Hi Dialists, > > Awhile back, researching machining on vitreous ceramics, I came upon the statement > that most rock/ceramic surfaces have a much lowered surface strength > when the > surface was alkaline and a much greater strength when acidic. (It was > in a NASA > report, but I don't remember the number ) Experiments showed that indeed drilling > speed was up to 7 times faster on alumina ceramics while in a solution > of a mild > base such as borax than on a neutral surface. A mild acidic solution > such as boric > acid doubled the time of drilling. Shear testing and microcrack examination showed > that the acid surface actually was both stronger and healed many microcracks. Even > mild acetic acid made a great degree of difference. > Shaping with sand-blasting obeyed a simular effect. i.e. The surface chemistry of > the etched lines and their surrounds may be acidic enough to hold up to erosion > longer. > > Just a thought. > > Edley McKnight > > - > - -
