tealyn Posted February 19, 2012 Share Posted February 19, 2012 I was wondering if it is better to have the trilobite positive and negative pieces for restoration than just the positive side. I noticed that many of the trilobite specimens on ebay come with both sides and was curious what purpose the negative side has in the preparation process. Link to comment Share on other sites More sharing options...
Wrangellian Posted February 19, 2012 Share Posted February 19, 2012 (edited) Some fossils don't come apart cleanly, and if the negative has some of the 'shell' of the fossil, then preparators can glue them back together and prep from the outside of the rock down to the outer surface of the 'shell' and it will be intact. I don't know what yours looks like, but if all the shell has remained intact on one side, then sometimes it's just nice to have the neg to show beside the pos, maybe to show it came out of the rock cleanly. If there was no shell (some fossils are just a cavity in the rock where the shell has dissolved out of), then both sides can be used to make casts of the original shell/carapace, either separately or put back together to make a mould in which to pour plaster or some such casting material. I dont know if this is done with trilos, but even if it is not, then what looks like the 'neg' will show you outer surface details while the 'pos' will show you inner surface details. It's not always easy to tell if you're looking at an outer shell/natural cast surface or the inner mould, so best to keep both sides in case. Clear as mud, I know, but hope it helped some. Edited February 19, 2012 by Wrangellian Link to comment Share on other sites More sharing options...
Bill Posted February 19, 2012 Share Posted February 19, 2012 It also shows straight away that the positive isn't a fake, as it will fit perfectly in the negative. Easier to fake a + than a -, I would imagine. KOF, Bill. Welcome to the forum, all new members www.ukfossils check it out. Link to comment Share on other sites More sharing options...
Wrangellian Posted February 19, 2012 Share Posted February 19, 2012 Good point. I guess it would be more trouble to make a fake + and - than just a fake +. Link to comment Share on other sites More sharing options...
richardfulton Posted March 16, 2012 Share Posted March 16, 2012 Often the impression (negative) is the imprint of the actual object (and may even be the original chiton, shell, etc.) while the mold (positive) is a cast of the INSIDE of the shell or object. This is different than, say in the case of mineralized fossils, wherein the object itself has been replaced as a whole. Link to comment Share on other sites More sharing options...
Wrangellian Posted March 21, 2012 Share Posted March 21, 2012 Good point also.. Tealyn must be thinking of the Bolivian trilos. If this is the case (original carapace/shell not there), then it is important to keep the mold (neg) as it will show an impression of outer surface detail that will not be present on the "pos" (interior mold). Link to comment Share on other sites More sharing options...
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