1. Prepare the base of the lap for the Pitch.
I used the pyrex tool blank for my lap. If you made a tile grinding tool, you will also need to make some sort of lap. Multiple layers of plywood work well.
Clean the surface of the tool and place aluminum foil around the perimeter of the tool. Extend the aluminum foil at least an inch above the surface. Tape the foil around the edge just below the edge of the glass. This will be important later. Have everything good and tight, we don't want hot pitch running off the lap and onto the table, floor, etc. Be sure that the lap is level also.
2. Melt the Pitch
Do this slowly, and preferably in your garage or outdoors. The smell of pine type pitch is lovely to me, but most people not involved in making the scope are going to get plenty annoyed. If you have to, you can heat it in the kitchen, but you may be single soon if you aren't already.
The softness of the pitch is very important. When the pitch is completely melted, take a bit on a spoon and let it cool to the temperature you will be polishing at. You might keep a glass of room temperature water handy to speed up the process. Just dunk the spoon in when it is just hard enough to hold its shape for a few seconds.
When the pitch in the spoon is at room temperature, take your thumbnail and press down firmly on the pitch. If you can make a dent in the pitch after 10 to 15 seconds, it is probably soft enough.
If the pitch is too hard, add some mineral oil to it. Use around a tablespoon per pint of pitch, then test again. Repeat if necessary. If it is too soft, just keep cooking it until it passes the thumbnail test. Some folks add some turpentine also. Don't add too much though, Turps softens things up more than mineral oil. The finished lap will harden up faster also if turpentine is used. I also don't like the idea of boiling pitch. Remember that pitch is a flammable substance
3. Pour the Lap
When you have the pitch at the right softness, pour at least 1/4 inch, and not over 1/2 inch of pitch on the surface of the lap. Make sure there are no leaks running down the sides. I have occasionally gotten bubbles on the surface. Don't worry about that.
Go have a beer. Let the lap sit for a few hours.
4. Press the Lap and Channel the Pitch
When the Lap is cooled and stable at room temperature, you are ready to press and channel the lap. Channeling is another part of lap making where everyone seems to have a different method. Mine is as follows:
Fold the aluminum foil down to just below the pitch / tool interface. This should be right at the tape line you made. This will keep the side of the tool clean during the channeling step.
Prepare a release solution of 1 cup water, 1/4 cup cheap dishwashing detergent, and 1/4 cup Cerium Oxide solution. If you use powdered Cerium Oxide, use 1 to 2 tablespoons.
Put the lap in warm water, around 105 degrees F. Do the same with the mirror.
After both are warm, place the lap on your work surface. Brush the release solution on the lap, then place the mirror on top the lap.
Move the mirror around to push the pitch in the direction needed. The pitch will move around a bit as you do this.
Stay with the mirror! You will press for around 5 minutes or more, but if you leave the mirror and lap alone for very long, they will likely get stuck. I have done this twice.
Repeat the process as needed. The pitch will probably work its way out the sides of the lap and will not quite come into good contact at the center. Dont worry about this too much yet.
Lay out a grid of squares on your lap using a pencil and ruler. The size of the squares depends on the size of the mirror. I used 2 inch squares for my 12.5 inch scope. 1 or 1 1/2 inch might be good on a 6 or 8 inch mirror. Do not center the squares on the mirror, us a little offset in each direction. I'm told centered squares will contribute to "regular errors".
Get out your trusty soldering iron. Heat it up, and draw it along the lines you have drawn on the lap, removing the pitch in that area. Tilting the lap will help the pitch run easily. Be sure to have some more aluminum foil underneath the lap for the hot pitch to run onto. This will take a while, so be patient.
After you are done channeling, cold press the mirror against the lap with a piece of nylon netting between the mirror and lap. This will impress little hexagonal lines into the pitch that will improve the polishing action.
At this point, I take my soldering iron, and holding the iron vertically against the edge of the mirror, I trim off the edges of the pitch. The triangular cross section of the iron tip cuts into the pitch at an angle, and makes a slightly undersize lap. This seems to help avoid the dreaded "turned down edge", the bane of ATM'ers.
It is also a good method for reducing turned down edge, of which I had a whopper at one point. But more on that later.
Next, after you are sure that you are done with melting pitch, peel the aluminum foil off the side of the mirror, and you will have nice clean sides on the lap.
If the mirror and lap are not in "perfect" contact by this time, you can start polishing anyhow. The two will soon come into good contact with each other, and we are just trying to put a good polish on the mirror, not figure it yet.