For those kind of tile projects, we would generally suggest our
GlassCast 10 Clear Epoxy Casting Resin as it is a great product for that kind of tile work. It can be cast in a single layer around 10mm thick or in multiple layers depending on the look and finish you are trying to achieve.
In essence, the number of layers is down to your artistic desires and limitations of the resin itself. With the GlassCast resins, the number loosely relates to intended casting thickness. In your case the GlassCast 10 is perfectly fine in multiple pours. For much thicker pours, GlassCast 50 is the one to go for. (it is basically the same resin as GlassCast 10 but with a slower cure hardener to prevent heat damage from exotherming).
Pigments is again, down to personal choice for the effect you are trying to achieve. We have a range of solid colours, tinting pigments and also Pearl Ex Metallic effect pigment powders . You can also go for metal cold casting with real metal powders or even a mix of all the effects. This picture is a sample piece we did and is only touching the surface of what can be achieved (in this case with multiple layers):
Any surface for a mould needs to ideally be smooth to give a good finish. Most surfaces will need a release agent to prevent the resin sticking, so we generally tend to recommend using mould materials that are non-stick suck as Polypropylene sheeting and/or premade silicone moulds.
You can drill the cured resin no problem using a HSS drill bit and carefully start using a pilot hole and open it up.
Warren PenalverEasy Composites / Carbon Mods - Technical Support Assistant