I have read articles on the net and in books on how to make a tile tool. I have tried a variety of methods and they all seem to do well:

http://www.johnstelescopes.com/HTML/TileTool.htm
http://www.kupercontrols.com/tiletool.htm
http://www.stellafane.com/atm/atm_grind/atm_plaster_disk.htm
http://www.atm-workshop.com/tile-tool.html
http://bobmay.astronomy.net/mirrormaking/mkplaster.htm

I have settled into the following method for creating a tile tool. This seems to work for me. Please feel free to provide comments and/or feedback. Please note, that I don't take any credit on the following procedures. This is simply a rehashing of a combinations that I have learned from the links above.

Making the Tool

	Place a trash bag or something similar to protect the work surface underneath. Place the mirror face up on the trash bag.
	Wet the top of the mirror. This will allow the foil to stick to the mirror.
	Place some aluminum foil on top of the mirror and wrap the foil over the edge. Do NOT wrap the foil underneath the mirror! This will make the mirror be unbalanced and could cause it to tilt when pouring which is bad.
	I used a manila folder cut into 4" high strips and taped them together. This is used for the dam to prevent the plaster to pour over the side. This works very well.
	I also use a pipe clamp. This helps keep the plaster from running around the mirror (usually not a problem if you mix the plaster/hydrostone properly). I place the top of the pipe clamp to about even with the top of the mirror. Make it snug, DON'T OVER-TIGHTEN!!
	I use Hydrostone to make my tools. It is water resistent and gets rock hard quickly. You use 32 parts water to 100 parts Hydrostone by weight. For example, for a 6" mirror tool 1" thick, I use about 1.5 lbs of Hydrostone to about .5 lbs of water. Hydrostone is available in 50 lb bags which fill a 5 gallon bucket nicely. Make sure you get a lid that will seal to prevent water in the air from getting into the bucket.
	I recommend going outside to mix. It gets messy. Also, Hydrostone is an irritant. Don't breath it in and protect your eyes.
	Mix the Hydrostone slowly and evenly into the water. Stir well.
	The texture should be pretty smooth once you are done, similar to pancake batter (sometimes I have made it a little runnier and it still works). Make sure there are not any lumps.
	Pour the Hydrostone mix into the mold.
	After about 10-20 minutes, it should be ready. You can tell by looking at the surface of the mixture. If it is still reflective, it needs to cure a little more. Remove the dam and slide the tool off of the mirror once it is dry to the touch. If the tool will not budge, turn the mirror over so that it is on top. Slide a rounded metal object (rounded putty knife would work) between the tool and mirror and slowly break the seal.
	There will be an "anti-bevel" from the bevel of your mirror. Use a metal straight edge to bevel the tool on the top edge.
	Put the tool on a cooling rack overnight to cure.

Sealing the Tool

	Score the top, sides, and bottom of the tool to allow the epoxy to stick to the tool better. Wipe away all the dust and make sure that all the surfaces of the tool are clean.
	Here are the supplies, a disposable cup, epoxy (I use the slow setting kind), stirring stick, 1" and 1/2" foam brushes. I used a roll of tape underneath the tool to enable application of the epoxy to the sides of the tool. Place the tool CONCAVE side down. The back of the tool will be facing up.
	I cut the disposable cup in half and put all of the epoxy into the cup. Stir the epoxy very well. This is important!!
	Use the 1" foam brush to apply the epoxy to the top of the tool. Go ahead, be generous with the application (just be sure to leave enough for the sides of the tool.)
	Apply epoxy to the sides of the tool with the 1/2" brush.
	Tool is now left on the role of tape to dry for 24 hours.

Adding the Tiles

	Here is a picture of the tile I bought from a local Daltile dealer. I bought a sheet of 1' by 2' Hex and Square porcelain tiles. These things are freakin hard! Both sheets cost me $11.00.
	Place the tile on top of the tool to get an idea where they will be laid after the epoxy has dried. Make sure that they are off center a little. Use a pencil to mark the location if desired. These tiles are stuck together by some rubber cement or something. I used my Leatherman to cut the tiles away.
	Just like sealing the back and sides, I cut a disposable cup in half and put all of the epoxy into the cup. Again, stir well!!!
	I poured some of the mixed epoxy on top of the tool. (You can see my pencil marks from the test tile placement.)
	Using the 1" foam brush, I brushed out the epoxy so that there is an even coat.
	Carefully place the tiles on top of the tool.
	Let the tool dry for 24 hours. Once that is completed, you now have a tile tool!!! Start grinding away!