well shrinking stuff is exact science if done properly there are very specific ratios of silicon to mineral spirit or you can get uneven shrinkage....
But I am a wee bit more gun hooo!! I basically mix my resin.. and and tip some white spirits in I am a proper butcher. the Mould can take 3 or 4 weeks to shrink... There is a tutorial someone sent me a link to ages ago but I am sure I can find it if I look my friend.