Mix .69 grams of powdered agar with 50 ml of water. This proportion should be accurate for most powdered agar; if your package states differently, however, follow the instructions on the package. This makes enough agar to fill five small petri dishes.
Dissolve an agar tablet in 50 ml of water. This proportion should be accurate for most agar in tablet form; if your package states differently, however, follow the instructions on the package. This makes enough agar to fill five small petri dishes.
Loosen the cap or lid on a bottle of agar slightly. Place the bottle in a hot-water bath. Because agar gels at room temperature, you must bring it to approximately 85 degrees Fahrenheit to return it to liquid form. Leave the bottled agar in the hot-water bath until it becomes liquid.
Open a sterile petri dish and pour your agar solution into the bottom portion. Fill the petri dish with approximately an eighth of an inch of agar. Return the lid to the petri dish and set it aside. Repeat this process for each petri dish that you wish to fill.
Leave the filled agar plates alone for at least an hour or until the agar has gelled firmly. Your agar plates are ready to use.