Re: Cloning vintage knobs
It is even possible to mould 'one off'* using plaster of Paris, provided you are moulding an item with a positive taper throughout its length (no negative shapes or undercuts) and with a flat back! Such a mould will not take resin unless it is thoroughly sealed, however and the item to be moulded must have a thoroughly applied release polish.
Another method is to mould with liquid rubber. This is a slow job as it is built up in layers, each needing to dry before the next is applied. Then there's Gelflex, a hot melt rubbery compound which is excellent but again tends to 'aerate' rather, and it stinks if you overheat it, something that is all too easy to do. Resultant moulds are very tough and long lasting, though.
I have cast resin into moulds and added a moderating compound such as French chalk or very fine wood flour to soften the hard gloss of pure resin. Along with colouring matter, cast knobs can be made to look and feel perfect.
*Removing the cast resin will almost always shatter the plaster mould.
Tony
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