I was told at a tile store (disclaimer: I was told something at a lighting store that turned out not to be very accurate) that to get the crackle finish, after the tiles are baked, a thin glass layer is added to the surface, heated at a high temp, then cooled quickly creating "cracks" in the glass, hence the "crackle" finish, and that it should be sealed. I do believe it should be sealed, as I had a sample of one where something had permeated a portion of the crackle surface, and it didn't appear there would be any way to clean it at that point.

Gloria, you use Delta Ceramcot's Two Step Fine crackle. You have to buy two bottles, step 1 and step 2. When the first one dries, you apply step 2. When it dries, the fine crackles are there, then you use any antiquing medium, or well watered dark brown paint, wipe off and the dark remains in the fine cracks. I have used it on clear glass plates which I decoupaged on the back .

Boy, using glue to crackle brings back memories of watching Aleene Jackson on TV. And as for polyurethane..... Polyurethane turning yellow has nothing to do with UV rays. There are 2 kinds of polyurethane - solvent based, and water based. The solvent based WILL turn yellow, and will continue to do so over time. Most people like this for refinishing furniture because over time it gives the wood a warm look. The water based poly will dry clear and remain clear. I have used water based poly for years on both indoor and outdoor wood pieces and have never had one of them turn yellow. I have some outdoor garden pieces that are years old and they have never yellowed. I have always used Flecto Varathane Diamond Finishes which are now known as Rustoleum Varathane Diamond Finishes. I highly recommend them if you want a clear and durable finish that will remain clear. You can take a look at the product here: http://www.rustoleum.com/CBGProduct.asp?pid=70

You seal the tile after it is installed but before it is grouted to prevent the grout from getting in the crackle. Just out of curiousity, what tile did you go with? I've been forever on the lookout for a crackle tile. Exactly right. Sue-- Try Distinctive Tile in York. I think you'll find what you're looking for. Tell em I sent you. (I just did some work for them a few weeks ago, and about to do some work for their Yarmouth store)