*1 piece of wood (eg. oak) of ~ 80 * 3.5 * 1 cm (32" * 1.5" * 3/8")
* 64 wine-corks
* wood-glue (preferable waterproof)
* wood oil
* Saw, preferable a jig saw
* Cutter knife
Time : takes about a day to complete : mainly because you need to glue a row of corks, and then wait for the glue to dry.
Step 1: Make a mold
It is very simple : cut a square hole out of a piece of leftover wood, eg an MDF board. If you want to make a lot of pot holders, you can cut several mold-holes out of the same board.
Step 2: Cut outsides - assemble frame
After experimenting, I've found out that the inside needs to measure 170 mm (6.7"). I guess that corks are about the same size all over the world, but to be absolutely sure I recommend that you double-check this : squeeze 8 corks in a row, and measure the lenght.
If you want to make smaller (eg 6*6 corks) or larger (eg 10*10 corks) pot holders, you need to adjust the numbers based upon this measurement.
In fact I think that a set of 3 pot holders, 6*6, 8*8 and 10*10 would make a very nice set :-)
If you have experience with cutting wood, you could make a miter joint, which will look more professional.
Then apply glue to the 4 pieces, place them into the mold : this will ensure that the frame is flat and square. Let it dry a couple of hours