MED’A Conjunctions is a blog-letter edited by Mary Ellin D’Agostino and sponsored by MED’A Creations.    Its mission is to foster education about metal clays and related topics.  Submissions, uggestions, questions, and comments are welcome.

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2 Responses to “About”

  1. jayne baume Says:

    Dear Mary
    I hope you can help. I am doing little investigation into the shrinkag of art clay silver when making rings with the PMC ring maker. I have found that fireing a long time increases the the shrinkage ( I am up to 2 hrs) which is what has been reported with PMC although I can not find much research on it. I believe you have done some investigation into this and I was trying to find your study but have not been able to, is there anyway I could read it. This investigation I am doing is simply for myself and the other instructors in new Zealan, so we can use the ring makers which are made for PMC and put together an accurate shrinkage table so we can get the strongest rings and the biggest range of shrinkage from each ring maker size. I hope this makes some sence
    Kindeat regards
    Jayne

    1. medacreations Says:

      The best info on the shrinkage of PMC can be found in the tech section of the PMC Guild website. Go to: http://www.pmcguild.com/gettingstarted/technicaldata.html
      Personally, I find that a ring made of PMC3 will shrink almost exactly 3 sizes. If you desire a particular size of ring, you should always use a ring insert so that the ring will not shrink beyond the desired size. Art Clay doesn’t like to talk about the increased shrinkage of ACS when fired longer/hotter than their official directions because they have committed to marketing their product as shrinking only 8-10%. I don’t know of any published data on the exact shrinkage of ACS products when fired hotter/longer, but you can use the information for the comparable PMC product as a close guide.

      The ring molds are usually good for about 3 ring sizes, but you might be able to extend that with experimentation. To test the minimum size possible, just make the ring as usual and fire it at 1650F for 2 hours–this will tell you what your minimum size will be for a particular mold. To figure the largest size, make the ring as thick as possible and try placing a ring insert 1 or 2 sizes larger than the ring mold is supposed to make and see what happens when fired at 1650F for 2 hours. The ring will shrink to the insert and then thin out as it shrinks in different directions. Make sure the final size is thick enough to be strong and did not crack during firing. I think trial and error are going to be your guide here. The manufacturers are probably a little cautious in their sizing suggestions because they want everyone to have a success, so it is possible that you can get a slightly larger size range from one mold.

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