Hi, apologies if this is in the wrong section.

I am looking to cast a polyurethane/polyester piece with a finish similar to this http://www.intertronics.co.uk/products/opt4220.htm.

The finish will be from 2-3mm thick and needs to be able to allow small LED's underneath the sheet to be seen from the other side.

As I am new to the world of casting, I'd like to ask if this finish is possible from just using a small amount of white colour pigment, or if I need to use a different kind of additive to the resin before casting.

Thank you.

You would need to experiment with the amounts of pigment to achieve the level of translucency that you desire.  From our experience you need around 5-10% to make the resin pretty much opaque to most light, so you would be looking below that level for your objectives.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant