Marcia Selsor Posted November 27, 2011 Report Share Posted November 27, 2011 Clayshapes, I have a book, Plaster Mold and Model Making by Chaney & Skee (ISBN 0-442-21515-0) but it may no longer be in print. Almost any book on the subjects will show you how to discern the parting line to get a two-part mold or show that you need more parts. Some years ago I was gifted "The Essential Guide to Mold Making and Slip Casting" by Andrew Martin ISBN 978-1-60059-077-1 which I've found useful to dip into .... it's very comprehensive and contains tables for mixing ratios and as well as recipes for casting slip Christine did this book mention Gauging plaster? Marcia Link to comment Share on other sites More sharing options...
Idaho Potter Posted November 27, 2011 Report Share Posted November 27, 2011 Marcia, I've used it to make two-part molds, and have close to two dozen plaster bats that I use for throwing--made these in 1985 and still use them. If finer detail is wanted, it takes extra care on the artist's part. The initial covering should be done while mixed plaster is thin and then, splattered on your postive model (dip fingers into plaster and flick it on to your original to make sure the plaster gets into detail--without bubbles--so the casting surface of the mold will be smooth. I could find no reference to "gauging" plaster in either of the books I own. No. 1 Industrial Molding Plaster is preferred for making molds, but if you need to take many pulls off the mold then, No. 1 Casting Plaster would probably be better as it has a hardening compound added to it making it more chip resistant. Both of these set up in 25 to 30 minutes (using a ratio of 100 parts plaster added to 67 to 80 parts water). Both of these can also be used to make models, but the hardening compound makes the casting plaster more difficult to carve. When making molds from plaster models, soap or some other separater MUST be used. Link to comment Share on other sites More sharing options...
Christine Posted November 28, 2011 Report Share Posted November 28, 2011 did this book mention Gauging plaster? Marcia Sorry, Marcia, no it doesn't .... and I've looked through my library, including the Potters Dictionary of Materials and Techniques - my default reference book! - and googled it too, and can only come up with "Gauging - A cementitious material, such as gypsum plaster, Keene’s cement or portland cement, added to lime putty to provide and control set" Sorry - not terribly helpful I'm afraid Christine Link to comment Share on other sites More sharing options...
gvb96 Posted November 30, 2011 Report Share Posted November 30, 2011 Hey guys, I'm doing this project out of sculpey and I'm wonderingabout how effective it is to use with plaster for casting? First time usingthis kind of clay and my professor's stumped about how it would work inplaster. I'm not worriedabout the condition of the original after but I'd like to reuse the clay so Iwasn't planning on baking it beforehand. It’s the original terracotta type ifthat matters at all compared to the firm and it'll be done as a 2-part mold. Thanks! Link to comment Share on other sites More sharing options...
Cymen Posted December 21, 2011 Report Share Posted December 21, 2011 I've researched Pottery Plaster versus Plaster of Paris some more and I found some interesting information on the USG website for plaster (Plaster.com): USG Moulding Plaster is the same as Plaster-of-Paris and is a great all-purpose utility plaster. USG® Moulding Plaster produces casts of nominal strength and hardness and faithfully reproduces the most intricate detail. Casts made of moulding plaster are porous and must be carefully sealed before decorating. For the Pottery Plaster mix, they have this to say: USG Pottery Plaster is famous industry-wide for working reliability, productivity and highly successful results. USG® Pottery Plaster is great for all types of ceramic slip casting applications. Pottery plaster is formulated for long life and reduced breakage (stronger molds). The dry strength is 2,400 PSI for Pottery Plaster and 2,000 PSI for Plaster of Paris. Based on this, it seems like Plaster of Paris should work fine for learning how to do molding and for molds that will only be used a couple of times. Once the technique is down and one wants a heavier duty mold the Pottery Plaster is more sensible. Does anyone have experience comparing both to see if there is any difference in fine detail? The mold making book I'm reading (Plaster Mold and Model Making by Chaney) seems to suggest Plaster of Paris should work fine in terms of detail and it is only in terms of wear/endurance that there is a difference. Link to comment Share on other sites More sharing options...
kimiclay Posted December 21, 2011 Report Share Posted December 21, 2011 Being in the spatial field of clay i use the least amount of math possible mixing plaster - 1/3 bucket of water and start sprinkling handfuls in until the mountain- 2 inches approx stays put and doesnt sink. I use whatever plaster i can find. To the softer stuff like plaster of paris, i add a handful of cement(no sand no stone) to harden it a little bit. this comes in handy when sand casting at the ocean and using salt water instead of fresh water. 2-3 handfuls of rapid set cement-all is my favorite. Salt water & plaster makes an extremely fragile compound. Additions of cement get the mold home in one piece in the back of the car with the kids, dogs, and swimming paraphanalia. In the studio i take one casting from the mold and tweek/clean the design in clay and recast another plaster mold without salt water. Sand casting at the beach means Big molds and a lot of fun! Link to comment Share on other sites More sharing options...
Bobg Posted December 21, 2011 Report Share Posted December 21, 2011 I think the last time I bought plaster at the lumber yard it was $17/50 pounds. It has worked very well for me when I make a mold. Bobg Link to comment Share on other sites More sharing options...
shiro Posted December 24, 2011 Report Share Posted December 24, 2011 I love making molds and have made a fair few molds of various materials including plaster, I only recently started making molds for ceramics use tho. That info about using industrial plaster is very useful! We just ran out of potters plaster! For the mixing, I was taught how to do it properly, but never remember except my tutor used to say it should be the thickness of single cream. That advice seems to have worked well for all my plaster mixing so far. Also I'm too lazy to measure the volume of plaster I need, but I alway try to mix less and then just mix more if I need too as set plaster sticks to wet plaster just fine. Some books suggest casting in wooden boxes but I use sturdy cardboard boxes for casting in. A glue gun can seal up the gaps. You can cast a surprisingly large amount of plaster in a cardboard box! ^^ I think the best way of learning to use plaster is to experiment and not be too precious. You are gonna have some disasters but that's how you learn. So rip open those bags of plaster and get casting! Link to comment Share on other sites More sharing options...
clay lover Posted December 27, 2011 Report Share Posted December 27, 2011 Still hoping for an answer to Marcia's Question, how sturdy or absorbent is this type of plaster, gauging plaster? Is it tough enough to wedge on? Too soliod to carve? Would you use the 'quick set ' kind listed above, or the regular with a 60 minute set time? I am always a little leery of the softness of my potter's plaster molds and forms. , the edges of things want to crumble, and I am freaked about getting plaster crumbs in my clay works. Link to comment Share on other sites More sharing options...
clay lover Posted December 27, 2011 Report Share Posted December 27, 2011 Sorry, guys, I didn't see the 2nd page of this thread when I posted the above, and for some reason ,I can't delete the above post. Apologies. Interesting thread. Link to comment Share on other sites More sharing options...
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