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Masling

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  1. I've done quite a lot of casting both in resin and white metal. I started out casting about 50 years ago with liquid Araldite resin but silicone moulds didn't last long with Araldite. I have a home made vacuum chamber built out of half an upturned calor gas cylinder (about 9 inches diameter). It's upturned so it still has its original gas connection which is now the vacuum connection. It has with an upturned pyrex mixing bowl for the top (with rubber seal) so I can see what's going on. I use a sheet of quarter inch perspex as a safety shield between me and the pyrex just in case the pyrex implodes under vacuuum. It hasn't happened yet but better safe than sorry. However, I have now stopped using it for resin casting, as I've found it's better to mix and pour quickly but use a paint brush to make the resin go into all the detail of the mould. I still use the vacuum chamber to degas silicone rubber but I also use a paint brush on that to eliminate surface bubbles on detail. I use Poundland brushes and throw them away after one use. I suspect that prolonged vacuuming of silicone rubber can change its physical properties because of the different vapour pressures of its constituents so some will evaporate away more than others. I also now make my moulds, especially one part moulds, with a bund, as found in central heating oil storage tanks so that they can catch any overflowing resin which sticks like mad to just about anything you don't want it to. I'd agree with an earlier comment to avoid water like the plague with polyurethane resin, unless you want it foamed, but I'd also avoid cliches like the plague. As an aside, I once left the top off a bottle of Part A and it absorbed quite a lot of water from the atmosphere. I weighed it and by comparing with the weight of the bottle of part B I got a rough idea of how much water it contained. I then vacuumed it for a few hours and was able to remove most of the water and found it would work OK when mixed with part B. I wouldn't recommend this for a really important highly detailed casting but I couldn't bring myself to throw away a nearly full pack of resin. As another aside, I managed to resurrect my one week old Motorola Moto G mobile phone after its adventure in my trouser pocket in the washing machine, by an hour or two in the vacuum chamber. Two and a half years later it's still working.
  2. Your excellent tutorial inspired me to have a go at photo etching and to join this forum. However, I hit a problem. After exposure in the fingernail thingy I tried to remove the protective layer from the top of the resist and found that the resist peeled off with it, both hardened and non hardened. What have I done wrong? A few possibilities come to mind. 1. I didn't expose it for long enough 2. Trying to take the protective layer off too soon 3. Not managing to get all the air or water squeezed out 4. Not cooking it enough in the laminator 5. ??? I looked at a couple of photo etching tutorials on Youtube and noticed a couple of things they do differently. Firstly they don't use a blob of water but apply the film directly to the metal. Secondly they don't use a folded sheet of paper to protect the metal and/or the laminator and they run the metal and film through the laminator three or four times. So I tried their way. The first thing I found that it was much harder to apply the film to the metal without creasing it or getting it to stick to itself. Based on my experimental sample size of one I can't be sure whether this was just a coincidence. The second thing I found was that after four passes through the laminator it appeared that the heat had made the film bubble up in places. On the plus side I found that I could easily remove the protective film, even before exposing to UV, while leaving the photo resist in place undamaged on the metal (apart from the bubbling). Any ideas how to get it right without too many experiments?
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