Should I use liquid dye or mica powder for a translucent color?

Either one. Both Pigmently Liquid Dyes and Pigmently Mica Powder Pigments can give you a translucent color you can still see through, or a solid, opaque color. What decides it is not the type of pigment but how much you add. Add only a little and the tint stays translucent; the more you add, the more opaque and solid it gets.

So for a smoky, see-through black in an UltraClear Deep Pour Epoxy river, a blue tint over a rock inlay, or a translucent white casting, pick the pigment by the look you want. Powders add a pearlescent shimmer; liquid dyes give a flat, single-tone tint. For black, try the Dark Matter powder pigment or the Black liquid dye. For a translucent white, look at Porcelain White, Snow Queen or the White liquid dye.

Because the amount is what matters, test first on a small scale. If you are unsure, order both types, mix a small batch with a little pigment, and see which gives you the effect you are after. Testing also tells you the pigment-to-epoxy ratio you need, so you can order enough for the full project.

Pigmently Mica Powder Pigments: https://www.bestbartopepoxy.com/collections/epoxy-powder-pigments Pigmently Liquid Dyes: https://www.bestbartopepoxy.com/collections/epoxy-liquid-pigments