Note the adhesive cork bits added to the clamp. The spring isn't very strong either.
I calculated 250 ml of resin to be adequate for the first layer. I weighted it - it was more or less the same in grams - and added about 2% of catalyst. After an hour or so, it presented the viscosity of a strong gel.
You can see the enormous amount of bubbles formed, even after careful mixing. The good thing is that these disappeared slowly by themselves.
Covered it with cellophane and put it outside because polyester resin is quite nasty!