15 April 2012
Yes, paraffin will leave a caked carbon on your molds. Paraffin does that because it is a petroleum based product, The 100% synthetic 2 stroke oil will not do that.
Getting the carbon off is hard. If it is light, hot water and comet cleanser and a brush will do it . Heavy carbon requires some tricks. A long soak with penetrating oil then brushing followed by the comet and hot water brushing works pretty well.
It is very important to thoroughly remove all traces of the penetrating oil from your mold or the heat of casting will cause any remaining petroleum distillates to flow and vaporize into your mold cavity and cause bullet defects. This puzzles a lot of casters who think petroleum and bullet casting molds are compatible.
As an aside to this......I feel bad you may stop buying paraffin! Nearly 100% of all the paraffin and petroleum jelly (Vaseline) on this planet comes from the State of Pennsylvania crude oil. The poor state of Pennsylvania will miss your purchases.