Roger - I scrub out new moulds with dish-soap, or AJAX with an old toothbrush to get the preservative oil out of them. This is done under HOT water from the tap.
They/it, once dry can now be used. I pre-heat the mould on the edge of the electric pot as the lead is coming to temperature. After use,
I sprayed them with WD40 and store them, even if soot coated. I re-soot the moulds before heating and use (for not moly coated mould blocks)
Before using the electric pot, I used to heat the mould beside the heat source I was using. The mould has to be hot, as-does the lead. Different
alloys require different heat levels for proper casting. Bright and shiny are pure lead balls.
One further step I now do, is I dry the mould after cleaning then spray them with a moly bullet lubricant coating- currently using Lyman's Super moly spray.
I have used MS Moly, but I'm out of that product so am using Lyman's - it works the same as a mould preservative and surface lead does not stick to. Rapine
used to sell a mould release coating which was a liquid graphite, seems to me. It also worked, but they are no longer in business, me thinks.
Also, the spray coating does not need oiling with WD40, so those moulds, I do not spray with that oil.
These mould blocks are moly coated.