Step one

Mix all of the ingredients together in a pot in the amounts above, and stir until agar and glycerol dissolve in the water.

Step two

Put the pot on the stove and heat the mixture to 95^o C or to just below boiling. Keep stirring the whole time.  When it reaches 95^o (or begins to froth), remove from the heat.  Keep stirring and skim off any of the froth from the top with a spoon.  Any froth left on the surface will cause air bubbles in your plastic sheet.

Step three

Pour liquid onto a flat surface or mold.  A silicon sheet works well with a frame (you can cut this from scrap wood), or alternatively, lay a silicon sheet on a baking tray with edges.  Let dry for 1-2 days, depending on temperature and humidity levels.