Information on our New PVA Mold Release
While the particular polymer used in the LM-3 lap mold separates very easily from the finished pitch lap, a number of mold releases have been considered that could further improve the process. This is particularly helpful in the so-called "overpour" areas, where users intentionally pour for a diameter greater than the tool, to ensure that the lap has good pitch squares to the edge. Traditional mold releases, such as silicone sprays, are miscible with the upper surface of the pitch, and produce a gooey pitch layer that considerably complicates polishing. Vegetable oil sprays, as well as any petrochemical derivatives, suffer from the same drawback. We discourage the use of any of these classes of mold releases. A user of the LM-3 pitch lap (Eric Sharader) has reported on a polar (water-based) mold release that does not interact with the pitch, but significantly improves the stripping process. We have tested the material, which is an aqeuous mixture of water, ethyl and buytl alcohols, and polyvinyl alcohol. It can be sprayed on the lap mold prior to the pitch pour, and dries to form a layer of polyvinyl alcohol that provides a very effective release agent for both the pitch lap itself, and subsequent removal and recovery of excess pitch from overpour areas. This mold release is completely water soluble, and any residues present on the finished pitch lap dissolve rapidly in running water. Our testing process has confirmed the value of this release agent, and we are now making it available to our users. It is provided in a 2 oz. spray bottle that has a very effective mist output, and can pre-treat your LM-3 lap mold over 50 times.
Directions for using the mold release:
It's quite simple to use: hold the spray bottle about 15" from the center of the LM-3 lap mold, at an vertical inclination of roughly 45 degrees, and pump the spray head several times (once it is primed and begins to spray). Rotate the lap mold by 90 degrees and repeat until all four orientations have been covered. There should be a thin film of the spray compound visible on all of the mold surface. Allow the lap mold to air dry for twenty minutes; when fully dry, the release film will no longer be visible. Pour the pitch into the LM-3 lap mold as described in the "Instructions for using the Perfect Pitch lap mold" section of this web site, being careful to avoid heating the pitch much beyond the temperature at which it flows freely. Once fully cooled, the lap mold will now strip off your lap with very little effort, and removal and recovery of any pitch overpour will be that much easier. Any PVA present on the surface of your pitch lap can be easily removed by simply holding the lap under running water; this is usually a good idea anyhow (using warm water) to slightly soften the pitch in preparation for warm pressing. If, as suggested in the Instructions page, you poured the pitch lap with the LM-3 laying on the primary mirror, then the lap curvature should be nearly perfect to begin with, and polishing can commence within a few minutes of the warm press. If a protracted period is likely between the next use of the mold release, you may wish to unscrew the spray head and purge it with tap water before replacing it on the spray bottle.
Safety Issues:
This PVA mold release is mostly a mixture of water and ethyl alcohol (to speed drying time). There is some butyl alcohol, which is added as a denaturing agent. The polyvinyl alcohol that actually forms the film is quite safe, but the whole idea of denaturing agents is to make the compound slightly toxic so as to discourage its ingestion as an intoxicant. Needless to say, that would be a very bad idea, and the mold release must not be consumed orally. Make certain that the spray nozzle is directed away from you before pumping. If you get any in your eyes, immediate washing of the eye and prompt medical attention is required. A materials safety data sheet can be examined here:
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