May I offer my slightly satirical observation on the use of resin moulds. I refrain from the use of the word advice as I do not consider myself qualified in this field, for this I would suggest you consult some fibreglass companies who can offer advice on casting a various range of resins. I do however have experience in casting, and particularly in the context of Oscar Wildes definition of experience, being the name we give to our mistakes! In that context I have significant experience. For casting resins I used to make boats, but moving to my hobby I tried casting the stuff to make pen blanks. I have to admit that the results were at best revolting and my thirteen year old sons semi chewed rhubarb and custard sweets had more artistic appeal than the bar of yuck that emerged. It was expensive, it was smelly, the results at best were awful and the resulting pen was a waste of a good kit. I have several acquaintances who proclaim the beauty of their plastic creations, I'm afraid I fail to share their enthusiasm for the procedure or the outcome. There are some resin blanks that are superb in both colour and turning texture, and there are others which are not. I have rationalised the equipment and stock that I had to make resin pen blanks with he use of a black plastic bag and the local authority dust cart, I now email George, they are smell free, always beautiful and turn fantastically!
If you haven't gathered it I'm not a fan of DIY blanks!