- Prepare a 2% solution of agar.
- Mix 20 g of agar with 1 L of distilled water.
- Heat almost to a boil. Stir frequently until solution is clear.
- Remove from heat and add 10 mL of 1% phenolphthalein solution
- 1 g phenolphthalein in 100 mL 95% ethanol (If pink, titrate with HCl until clear)
- Pour agar into a shallow tray to a depth of 3 cm and allow it to set (over night).
Silicone Ice-cube trays can be used. It is difficult to find them in the appropriate metric measurements. 3 cm cubes are approximately 1.2 inches and there are molds for this.