Page 18 - ArtMolds Journal June-July 2103 Mod 4
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  LIFECASTING  If It Looks Like a Duck... Or How to Cast a Complete Arm in the Round Without Distortion  By David E. Parvin, A.L.I. N a block mold is its simplicity, saving time in construction. The disad- ot long after I began ex- vantage is that a block mold will perimenting with life require more of the molding materi- casting in 1987, I tried something which seemed logical, als which can be pricey. Over the years, I have been but in fact didn’t work. I had suc- able to cast decent entire arms and cessfully cast some hands and feet legs using skin molds. Because by immersing them into containers filled with alginate. Obviously, I rea- soned, I could simply get a taller   container and cast a whole arm the same way. Squashed But when I peeled off the algi- nate, the plaster fingers were flat- tened and reminded me of duck fingers can look bills. I was baffled at first but then suspected that what was happening was that the weight of the alginate a lot like baby was causing it to compress, the ef- fect of which would be greatest at the bottom of the column where the Photo 1. Life casting an arm using a skin  duck bills. fingers were. mold was a flop.  There are two common types of molds: block and skin, and each has advantages and disadvantages. What I am describing here is a block less alginate is used in a skin ver- mold so-called because the object to sus a block mold, it doesn’t want to be cast is simply surrounded by a compress under its own weight. “block” of some casting material But at the time I began this article I such as alginate, rubber, plaster, was discussing with a client a pos- etc. sible commission which would The construction is simple, just have required at least twenty pairs construct a wall around the object of arms, all forty of which would be and pour in the mold material and let unique. I decided to experiment to it set up encasing it in a “block”. The see if I could come up with an easy wall may also serve as a mother way to do so many castings. mold though if the molding material Since I had not done a skin is thick enough then a mother mold mold on a complete arm in some may not even be required. time, I decided to attempt one on a The “skin” in skin mold refers to volunteer’s arm to see how long it a much thinner layer or “skin” of would take (photo 1) and if there rubber or alginate which is painted were any unforeseen problems. In on in layers on the object. Over the the photo to the left, my assistant skin is constructed a conforming Photo 2. My assistant Jay’s boyfriend,  Steve is covering volunteer Jeff’s rigid mother mold which is neces- Alistair  is cast in the block mold method  arm with two layers of alginate. sary to hold the flexible mold materi- for verification of  duck beak problem.  Over that we built a two part al in shape. The main advantage of mother mold using fast setting den- June | July 2013 ARTMOLDS JOURNAL | 18 
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