Mold Making with Mold Mix 7
By Leslie Rowe-Israelson and Melanie Rowe
Edited by Brooke Hamling
Make sure the powder is in a container that can be properly sealed before mixing. Slowly add 4.8 lbs. (2.16 liter) of water to the one-gallon bucket, slowly incorporating the liquid with the powder. At this point the mixture will be very lumpy and contain pockets of unwetted powder. Next, take an emersion blender or a hand mixer and whip the mix until all lumps are broken down and the mix consistency mimics a thick cream. You will notice fibers in the mix. These fibers weave a blanket in the mold and add strength. The mixture should be left to set for 30 minutes before application. The mix will solidify if it remains uncovered for an extended period of time, but simply stir with a spoon, spatula, or mixer and the mix will regain its creamy consistency. Once again, keep all containers of Mold Mix 7 covered, even when actively applying.
Applying Mold Material to a “Wax Positive” for Lost Wax Mold Making
Take small container of pre-mixed Mold Mix 7 and paint on thin layers with a soft supple brush. The finish on wax positive will determine finish on art piece. If the mold material wants to separate do not worry, just keep brushing. Start applying the mix at top and move down project. Place your pattern covered with the first coat in front of a cool fan to dry. This initial layer must be tacky dry before applying the next coat. Think of drying from inside-out. If you try to apply the mix too thick it will want to crack. Do not let the mix build up thick in undercuts of the mold. Try to paint each layer in a different direction to weave a blanket over wax and use the fibers in the mold material. Keep painting on layers until you are approximately 1/8 to 1/16th inch thick. Any thicker and it may not allow sharp areas to shrink and it may break off small details like arms or fingers. Let the mold dry totally-approximately 3 days. If it is still cool to touch wait an additional day. Small molds may take only 2 days to completely dry.
Applying to plasticine (no burn-out necessary)
Paint on thin layer of Murphy’s Oil use soft and let dry. Paint on the mix in thin layers and let dry. It will start to curl on the edges but this is OK. If you have no undercuts the mold should be easily removed and you can start using your mold.
Microcrystalline wax is toxic when heated to burning. Burn out the mold with propane torch while wearing a respirator and take all necessary precautions including fire gloves, eye protection, etc. Burn outside on a day without wind. Get a metal garbage can and have the lid ready to put out any fire if the wax ignites. Fill the garbage can ½ way with water and place a steel rack on top. Then place your mold on top of the steel rack. Light the torch and put the torch on low. Point the torch to the bottom edge of mold, waving the flame from the bottom to the top. Keep the torch horizontal at all times. Do not point the torch directly into the can. Let it begin to drip slowly but continue to be cautious of the wax catching on fire. If the wax ignites, stop torching and let the fire drip into the water until it stops burning. Do not rush and do not worry if mold catches fire because it will. If wax leaches through mold material it will burn off during firing. At this point in the process the mold is very fragile, therefore be extremely cautious. Take the mold and gently put in a kiln and heat up to 1400℉ to return the mold to white. This material is resistant to thermal shock so heat the mold to this temperature as quickly as the kiln will allow.
Although no release agent is not a necessity, the recommended release agent for use with Mold Mix 6 is Bullseye Shelf Primer. It provides a wonderful release that will give you a soft stain finish to the glass wherever it touches the mold. Get a sifter and two. Make sure the mold is clean and sanded to a smooth finish. Vacuum the mold carefully and wear a respirator. Get a partner to help, and a large bucket ready to pour shelf primer. Mix 1 part of powder to 5 parts of. Mix well, then sift 5 times getting rid of chunks and foreign particles. Quickly after the last sifting (do not let the shelf primer settle) hold the mold upside down, pour in the mix, and then poor the mix out quickly and evenly. Do not let it settle in the mold and aim to achieve the thinnest coat possible. Speed during this procedure is extremely important if you have any bas relief or fine detail in your mold. Once this has been achieved put the mold back into the kiln and heat to 400℉ to burn off all the excess. You are now ready to use the mold.
Select a container that completely surrounds the mold. Our containment walls of choice are stainless steels tubes and or pots. We have found that steel tubs tend to break down at high temperatures and pits into the mold. Do not load sand without respiratory protection. Use dry 80-grit clean silica sand or olivine sand to fill the space between the containment wall and the mold. We burn out our sand before first use to eliminate any foreign material. Gently cover top of mold to ensure that no sand gets into the mold. Pour sand carefully and slowly into the container. Try to match the container with the shape of the mold so that the sand walls are consistent.
Choosing Attached Sprue or Drip pot
This step is your decision as each project comes with its own technical difficulties. You must think ahead while designing your piece. Will the glass flow into every space? Do I lay the pieces sideways, straight up or down? If I use a ceramic drip pot, I will surely capture bubbles as the glass drips down? Do I gently pour frit into my mold? Will I hit fragile points? All of these questions must be addressed before beginning the design.
Firing Schedule – a fine science
This will depend on your piece. You must carefully plan this part of the process before you begin, but here is a simple example firing schedule:
Take 10 hours up to 1010.
Hold 4 hours to heat sink sand
2 hours up to melting.
Hold no more than 2 ¼ hours.
Open face only 1 ½ (crystal flows faster than Bullseye. Frit must be ½ longer).
If intricate, narrow spaces-hold 2 ½ hours to 3.
Then continue rest of the program.
Removing the Mold
After Firing, the mold must be removed from the cast glass. If the mold is firmly adhered to the glass soak the mold in water to soften the mold. The small bits of mold mix that remain can be removed using a soft bristle brush, like a tooth brush, and water.