What kind of ink should I use on travertine tiles? I am making tile coasters for party favors. Stamping the tiles then coating them with Mod Podge. Should I use solvent or dye ink?

I have always heard to use stazon and then bake in the oven.

Use Stazon ink and the image will stamp beautifully.

I agree with Stazon! It works on practically everything and I use it on wood, ceramic tiles, glass...all kinds of stuff with total success as long as you seal it. I don't use Mod Podge often but read the label to make sure it won't get mushy when a wet glass sits on it. I usually use verathane to seal my items. get that at the hardware store for a better price usually.
Keep having FUN as it sounds like you are