Raistlin Posted August 23, 2012 Share Posted August 23, 2012 Okay so today I went to a friend's house and was using his air abrader/blast box. I was cleaning the stuff I have been finding at work. The stuff I have been finding at work is covered with weathered calcite (I am fairly certain that is what he called it) that can be cleaned off with little to no abrasive material. In several cases I was able to clean the stuff off with less than 5 psi of air. My question is though I have noticed the inside of the shells of bivalves and brachiopods are a lot more stable than the outside. Is there a reason for this? It seems that I have trouble cleaning the outsides without starting to eliminate a small amount of detail or causing pits (and this is with nothing but air I tested by running the flow over my fingernail and it left no mark). Is this common even in the more stable specimens? I admit that these specimens are a bit fragile in some cases the shells are paper thin nearly, yet still hold some great detail. I even tried to clean my cephalopod that I found at work and it started to remove some of the fossil, or at least it seemed. You can make out a bit of segmentation/suture to it now but I was afraid to do too much on it because just the air was removing too much it seemed. For instance I wrecked a very tiny (only seen it under microscope) gastropod. Some of it is left but the air tore it up pretty good. Again all of this was at less than 5 psi. I do not have a way to take photos yet of the microscopic stuff but I found some really cool things and detail while cleaning what I did. Later I will try to take some photos that at least show a bit more detail than they did before cleaning. I have this really amazing bivalve half that looks a lot like something I would find at the beach. I love it. By the way these are Ordovician in age and my friend believes they are Plattin formation and not Decorah formation. You can see the original thread on some of the finds here. http://www.thefossilforum.com/index.php/topic/30123-cephalopod-help/ Everything has been collected at night with a flashlight and only had to chase the skunk away once Thanks for your help. RobertSoutheast, MO Link to comment Share on other sites More sharing options...
erose Posted August 23, 2012 Share Posted August 23, 2012 Not sure if this is the reason, but, at least for brachiopods, the shell has a multilayer structure and can be porous as well. They generally are not as robust and homogenous as a large clam or oyster. I know I have brachs from the Ordovician that look to be very well preserved but upon closer inspection and comparison to truly complete ones the top most shell surface is missing. Again I have no idea how this relates to outside versus inside. If you can get your hands on a copy of the Treatise on Invertebrate Paleontology you can see better information on the "shell structure". Link to comment Share on other sites More sharing options...
Raistlin Posted August 23, 2012 Author Share Posted August 23, 2012 Okay thanks. I know before cleaning them you can see some good detail such as all the scalloping and the what I assume is the growth lines of the shell. As I started to run the air over them the outside started to remove and pit a bit so I stopped. The inside held up great though. RobertSoutheast, MO Link to comment Share on other sites More sharing options...
Malcolmt Posted August 24, 2012 Share Posted August 24, 2012 I tend not to use air abrasion even at low pressure on the brachs that I find, the results have never been all that great to warrant the effort, Link to comment Share on other sites More sharing options...
Auspex Posted August 24, 2012 Share Posted August 24, 2012 Have the hyper-fragile surfaces surfaces been exposed to weathering? I mean, 5 psi air, with no abrasive? "There has been an alarming increase in the number of things I know nothing about." - Ashleigh Ellwood Brilliant “Try to learn something about everything and everything about something.” - Thomas Henry Huxley >Paleontology is an evolving science. >May your wonders never cease! Link to comment Share on other sites More sharing options...
Raistlin Posted August 24, 2012 Author Share Posted August 24, 2012 Yes, unsure how long they have weathered. RobertSoutheast, MO Link to comment Share on other sites More sharing options...
Auspex Posted August 24, 2012 Share Posted August 24, 2012 Yes, unsure how long they have weathered. Might be part of the answer. "There has been an alarming increase in the number of things I know nothing about." - Ashleigh Ellwood Brilliant “Try to learn something about everything and everything about something.” - Thomas Henry Huxley >Paleontology is an evolving science. >May your wonders never cease! Link to comment Share on other sites More sharing options...
Raistlin Posted August 24, 2012 Author Share Posted August 24, 2012 True, I wonder why the inner part of the shell is more stable though? Seems odd that the outter sides are weaker. It is like they peel like an onion, yet the inner just cleans. RobertSoutheast, MO Link to comment Share on other sites More sharing options...
Bullsnake Posted August 24, 2012 Share Posted August 24, 2012 I would assume that the inside of at least most shell has greater density than the decorative (for lack of a better term) outside. Like if you take a modern mussel shell, and scratch the outide, it is easier than scratching the inside. Steve Link to comment Share on other sites More sharing options...
Raistlin Posted August 24, 2012 Author Share Posted August 24, 2012 Yeah I never thought of that. I wonder if it is like the outside of the shell as you say and is/was a slighty different material. I know you can scratch the dark color off modern shells and take it down to the same color of stuff the inside is made of. You bring up a good point I had not thought of. Thanks. RobertSoutheast, MO Link to comment Share on other sites More sharing options...
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