Ark Posted June 4, 2011 Share Posted June 4, 2011 Today I made my first attempt at metal casting. I was attempting to cast some scales for a straight razor out of pewter. Sounds pretty simple right? I made a mold out of plaster of paris and melted an old pewter statue I found in an old skillet with good pour spouts on my forge. Everything was going ok until i poured the molten pewter into the mold and it exploded everywhere. Luckily I walked away from the incident unscathed exept for my feelings. I let the plaster dry for 24 hrs, am I supposed to bake it? Also the pewter produced a lot of slag, can I fix that by coating the metal in borax? I did consult the magic search bar at the top of the screen before posting but turned up nothing so far. I appreciate your help fellas. Thanks Quote Link to comment Share on other sites More sharing options...
pkrankow Posted June 4, 2011 Share Posted June 4, 2011 First I am glad you are unhurt. I hope this was because you were wearing proper personal protective equipment (PPE) and not dumb luck. It exploded because of water, or retained investment material vaporizing. Baking out the mold and pouring into a hot mold is always a good option, as it provides insurance against retained water. I am unsure about how plaster of Paris tolerates heating to bake it out. I recall it becoming crumbly at a rather low temperature. Welcome aboard. IFI is a wonderful place with members from around the Earth. There may even be an organization near you that can provide some instruction and assistance. Phil Quote Link to comment Share on other sites More sharing options...
jmeineke Posted June 4, 2011 Share Posted June 4, 2011 from http://ladybethany.tripod.com/CASTING.HTM Plaster can work much the same as soapstone. Find a suitable mold to pour slabs of plaster (I use travel size baby wipes boxes and then cut the plaster in half). Once it is dry, sand the faces smooth and carve your design, spure and air vents. Before you pour the pewter, make sure that the plaster is completely dry (3 to 7 days and low humidity or some time in a food dehydrator) or the moisture in the plaster will expand when the pewter heats it and cause your mold to explode and/or pewter to spit back up and out of the mold. Plaster molds get hot when casting, so only cast 5 or 6 items in a row before you let the mold cool. The mold can be reused 20 to 50 times depending upon the original detail and how fast the plaster degrades. Good luck! Quote Link to comment Share on other sites More sharing options...
Fe-Wood Posted June 4, 2011 Share Posted June 4, 2011 Glad you were not hurt!!! Yes! you definitely want to bake the plaster at a low heat. Steam is your enemy!!!! All the investment casting I have done is with the lost wax method. Baked over night at above 500 deg. to vaporize the carbon left from melting out the wax. Then straight into the casting areas to be poured while the mold is still hot. I have used Cuttle Fish Bone, from the pet store for casting small parts in Silver. They are cheep and easy to get. I warm them with a plumbers torch a bit before casting. I have also used wood molds for pewter. Given Pewter melts at about the flash point for wood its a one off mold, so is Cuttle Fish Bone. You want to "toast" the wood before casting. Here is a really down and dirty mold for casting Pewter flat bars.... Also, Don't over heat the pewter.... Quote Link to comment Share on other sites More sharing options...
Ark Posted June 5, 2011 Author Share Posted June 5, 2011 Thanks for the help guys. About over heating the pewter, is the forge too hot for the job or should I use a different heat source? Quote Link to comment Share on other sites More sharing options...
pkrankow Posted June 5, 2011 Share Posted June 5, 2011 Pewter can be melted on a stove top fairly safe. The forge is fine. The melting point is a bit below 500F and the casting point is about 580F. Ventilation is very important. http://www.princeaugust.ie/alloys/ Now the exact composition is not stated. Fine pewter is tin+copper to saturation (about 1% copper). Various other materials called "pewter" are alloys of tin and lead, which can be problematic for food contact, but probably not for your current project of razor scales. A stand-in for pewter is lead free plumber's solder. It can be had easily in quantities suitable for small projects and it has a low melting point and pleasant working properties. Phil Quote Link to comment Share on other sites More sharing options...
781 Posted June 5, 2011 Share Posted June 5, 2011 Saw a couple people demonstrate pewter One used the cardboard from a toliet paper roll and the other used the cardboard from cake or cereal boxed Use paper tape not plastic ONe was pouring tomahawk handles the other knife handles Quote Link to comment Share on other sites More sharing options...
kcrucible Posted June 8, 2011 Share Posted June 8, 2011 Yes, you should be bringing the mold up to heat... ideally much higher than the boiling point, so that the pewter doesn't cool down instantly and not fill your mold fully. A borax glaze on the molten metal will help prevent slag. Quote Link to comment Share on other sites More sharing options...
Bentiron1946 Posted June 10, 2011 Share Posted June 10, 2011 Typically on low melt metals there is no need to use borax, I'm not even sure what the melt temp is on borax but I have found that if you have a bullet casting ladle where you are pouring from the bottom you will not have much problem with slag at all. Many years ago I got lucky and found an electric lead pot at an estate sale, it had a bottom dump for casting bullets and it is so great for casting small pewter doodads. I just slice the flask under the bottom dump and lift the lever and out pours a liquid stream of pewter into the mold. It is so nice and when I'm finished I can put my ingot mold underneath and empty the whole pot into approx. 1# ingots for the next time. I used to make my own investment out of 1/3 plaster of Paris, 1/3 hydro-call and 1/3 silica sand, it worked well but sometimes is prone to expansion cracks and can setup very hard. Any investment that uses plaster of Paris needs to cure until it quits producing it's own heat and then baked slowly until all moisture is gone. Cuttle bone leaves a very interesting texture but is not very good if you want a highly detailed carving. :blink: Quote Link to comment Share on other sites More sharing options...
Joe C B Posted August 22, 2011 Share Posted August 22, 2011 Hydro -call.... what's this stuff? I looked it up and it's "Gypsum Cement" So how is this different than Plaster of Paris? Joe B Quote Link to comment Share on other sites More sharing options...
Bentiron1946 Posted August 25, 2011 Share Posted August 25, 2011 The hydro-cal was used because it would set up really much harder but if you used all hydro-call it was really hard to get it off of the final casting(and was much more expensive), it also would pick up finer detail(fingerprints) but some use two thirds plaster of Paris and one third silica sand and if they are really on the fly, masons sharp sand. Quote Link to comment Share on other sites More sharing options...
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