While we have made Sylgard dishes ourselves, here is a bit more detailed procedure with a couple of tips:

Making Black Sylgard Dishes (Corwin, J. for MBL course).

Note: if the link goes away, here is the gist of it:

1. Mix sylgard per instructions (A 300g, B 30g, for example), mix. Do this in a disposable plastic beaker.
2. Weigh out 2 grams of Norit A Charcoal Powder and add that to the Sylgard mixture in the beaker. Thoroughly mix that in using the tongue depressor.
3. After the Sylgard has been fully mixed it can be carefully poured into the bottoms of the Kimax glass petri dishes. It is best to decant the Sylgard mixture into the dishes slowly using the applicator stick (tongue depressor) touched against the bottom of the Sylgard dish and the tri-pour beaker, pouring from one corner of the beaker slowly. Fill each petri dish bottom only about one-third to half full. NOTE: It is important to make sure that you fill the dishes to the desired level, so check several existing Sylgard dishes to determine what level of Sylgard is most effective for our microdissections. If in doubt please ask for help. It is also important that the dishes cure while on a flat, level, non-moving, and non-vibrating surface.
4. Bubbles will come up to the surface of the Sylgard after the initial pouring and it's important to get rid of them before the dishes cure. This is most easily done by using a small butane torch held about 10 to 12 inches above the dishes and aim it directly down to the surface of the Sylgard in each of the dishes that contain bubbles. It just takes a small amount of heat from the torch to cause all the bubbles to pop and disappear leaving a perfectly smooth surface. (Take care not to overheat the Sylgard).
5. After all of the dishes have been filled with the Sylgard, put their covers on to protect them from dust as they cure. Leave them on a level flat surface with a note saying "DO NOT DISTURB FOR AT LEAST 24 HOURS" so that they can cure.

If anything comes in contact with the Sylgard, let it cure at least 24 hours, then you can dispose of it in the trash.