Hello, I recently finished a large job where I sealed tumbled travertine. I recommend using one of the Tilelab penetrating sealers (Custom Products) that are linked to below. Either one of these sealers will be fine and will not change the color or natural look of the floor.

www.tilelab.com/ProductC...

www.tilelab.com/ProductC...

As far as technique for applying the sealer to both the tile and grout, I have tried everything from a paintbrush, to a squeegee, to using a roller brush. The problem with these methods is that it is very wasteful and tends to leave large puddles behind which have to be cleaned up. What works the absolute best is to use a SPONGE MOP. Not only will it save your pocketbook by using less sealer, but it will also save your back. Put the sealer in a pan and mop on just enough sealer to coat the tile and grout. Apply slight downward pressure so that the sponge head forces the sealer down into the little pits and recessed grout areas while eliminating puddles. Be sure to wipe the surface off with a towel before it has a chance to dry. It is good idea to use two people with this technique so one can apply while the other buffs dry with a couple of terry cloths or a dry mop on a handle. Good luck.