-Furnace or kiln that can heat up to at least 800° C (1500° F)
-Ceramic mold for glass casting (examples found here)
-Glass separator (also known as kiln wash) (example found here)
-Small scale to measure ingredients
-Proper safety equipment for working with chemicals (ie gloves and a disposable respirator) and with the furnace
-Dremel tool (optional)
Step 1: Mix Ingredients
Borosilicate glass is composed of sodium oxide (Na₂O), boron trioxide (B₂0₃), and silicon dioxide (Si0₂). To get this final composition, we will be mixing sodium carbonate, boric acid, and silicon dioxide.
Amounts to make 100 g of glass:
Boric acid 49.11 g
Silica 47.73 g
Sodium Carbonate 42.10 g
Weigh out the proper amount of each material based on how much you want to make. Note that the total weight will be greater than 100 g because some chemicals will evaporate in the melting process.
Mix them together thoroughly (Tip: This process can be automated using a very clean, well sealed rock tumbler and some steel balls)
Material Data Sheets:
Refer to these documents for important safety information
Step 2: Prepare Mold
0. If in powdered form, mix with water as directed
1. Brush onto mold in long, even strokes, covering the whole mold in an even layer
2. Let dry and rotate 90°
3. Repeat at least 3-4 times
4. Heat empty mold to 300° to ensure there is no remaining mosture
Step 3: Make Glass!
Put the empty mold in the furnace or kiln with the following heat cycle:
1. heat slowly (< 600°/hr) to 800° C
1.1 add a small pile of powder to the center of the mold
2. hold at 800° C for 12 hours
2.1 add small doses of powder to the mold while at 800° C every 20 minutes.
3. cool slowly (~ 30° / hr) to 500° C
4. hold at 500° for 2+ hours
5. cool slowly to room temperature (~ 60° / hr).
Important: Do not open the furnace during the heat cycle, except to add powder. Thermal shock could cause the mold to crack or shatter.
Step 4: Extract Glass
In theory, the mold release should cause the glass to fall out when inverted, but it often doesn't work that well. Instead, find a weak point in the glass at the corner of the mold and use a small chisel or flathead screwdriver to start prying out the glass. Be careful not to break the mold! Water can be used to wash away the dusty kiln wash away as you go.
Step 5: Finishing
Examples of glass art projects:
Mixing raw powder
Further glass working techniques