I have been making some tile coasters as gifts and I'm no expert, but I do have some tips to share.
I have purchased the unglazed tiles at Menards and Home Depot. I found that some of them were covered with a fine powder-like dust. I washed them in plain water, and rinsed them well, and then left them to air dry. I leave them dry a day or two, if possible. I learned that if I put them back in the boxes they came in, they picked up more dust again, so I stopped storing them that way.
For most of my tiles I stamp with black StazOn ink. To my surprise the more detailed the stamped image was, the better. Again, allow them to dry for a day or two. I have been able to speed the ink drying process along, by using my heat gun on them. I found if the ink was not totally dry, it would smear when I was coloring them.
I color the images with Q-tips and more StazOn ink. I do pick up the color from the stamp pad, but I found my favorite way to color was to use re-inkers. I drop a drop of the reinker on an ice cream pail lid and then use Q-tips to color my image. I purchased a number of reinkers and just skipped buying the pads, since I don't think I will be stamping with most of the colors. I was able to make tints of colors by mixing the white reinker and colors. I would think that you might be able to mix two colors together, but I haven't actually tried that. I have also used makeup sponges to sponge a sky or other background color.
The tiles/ink are not very forgiving if you goof. I did try to remove a little smudge with StazOn cleaner, but I didn't have a great deal of success. I didn't work at it too much, because I was worried I might just make it a bigger problem. I totally messed up a couple and now I use them to practice different techniques.
I bake my tiles at 300 degrees for 20 to 30 minutes and then shut the oven off and let them cool in the oven. I add cork to the bottom with E-6000 glue and have also put the little furniture protector felt circles on top of the cork. My DH thinks that is overkill but I feel better knowing there is no way it will harm furniture.
I had my DH take some pictures but haven't had her home long enough to get her to get the pictures off the camera and uploaded to SCS. I don't know how well they will hold up, but the ones I have been using in my craft room are doing great and they have not even been heat set. I don't use sealers of any kind. I was told last week that they can also be colored with VersaCraft ink and chalk inks, but I haven't tried either method. This summer I plan to stamp tiles for an outdoor table that will be exposed to all kinds of weather. I can't wait to see how that works out.
I hope this helps you a little. I would love to see pictures of your finished tiles and I will try to get mine posted soon. Good luck!