Reproduced with permission of the publisher of Lapidary Journal, January and February, 2007, Volume 60, Nos. 10 and 11.

• Metal models ready for molding
• Mold frame (5/8" high x 1 7/8" wide x 2 7/8" long interior dimensions).
• Vulcanizer
• Two mold frame plates, large enough to
sandwich the frame with more than 1/2"
extending all around.
• Mold pressure plates (.064" thick and
.032" sheet cut slightly smaller than
1 7/8" x 2 7/8" with rounded off corners)
NOTE: Cut up 4" x 10" sheets of K&S
aluminum available at hobby and hardware stores.
• Old rolling pin or 12" dowel,  diameter 1" or more.
• Steel ruler
• X-Acto® knife.
• Pointed tweezers (AA or similar).
• Sprue base formers (commercial or handmade).
• Sharp scissors.
• Soft bristle brush for spreading powder
• Fine brush (00) for powdering release vents.
• Dull, round-tipped, nonserrated butter knife.
• Scalpel with #11 blades.
• Heavy Duty aluminum foil (Reynolds is
thicker and better).
• Baby powder or jeweler’s talc.
• Wax paper.
• Indelible felt-tipped marker (Sharpie®)
• Ziploc® freezer bag (quart size)
• Small covered container(s)
• Denatured alcohol and paper towels.
• Silicone rubber (Castaldo® Super Strength Strips.™)

      Powder separation moldmaking techniques can be used by moldmakers of all experience levels. For some, powder separation means entry-level with no scalpels (except for cutting air releases), consequently less danger of injury. For others, it means convenience, speed, and tight registration. I will be covering just two types of powder separation molds in this article. The first mold will be made with pre-vulcanized keys (instead of commercial metal “locks”) and powder separation. The second mold will combine pre-vulcanized keys with powder separation and hand cutting. Modelmaking will not be covered in this article.

The preparation.
Prepare your frame by dulling the edges of the opening with a sanding stick, because some of them come with very sharp milled edges that can seriously hurt you. You don’t want bevels, just smooth, non-cutting edges. You do, however, want to cut a bevel on one exterior corner of each side of the frame. This gives you a spot in which to slip a dull butter knife to pry the plates from the frame. Mark the frame with a diamond ball bur or a Dremel® electric engraver. Write “silicone” and “top/front” on one of the faces. This is important because the molds should be dedicated to only silicone rubber or only organic rubber, and it’s helpful to know which side the front of your model faces.

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