How to Crack Insulators

Electric lines once used glass insulators to connect wires to the pole.

Insulators were a regular sight on telephone poles until about 1970, when porcelain insulation and buried cable took over. Glass manufacturers used recycled glass to make insulators for telephone and telegraph poles, so the colors are often shades of green. Insulators became collectible by the 1980s, and cracking insulators was popular to make them more decorative. Insulators crack with fast changes in heat and cold, much like marbles. Those made of clear glass look like chipped ice.

Things You'll Need

• Metal pan
• Insulators
• Oven
• Oven mitt
• Gallon bucket
• Ice cubes

Instructions

1. Select insulators that have no significant value as collectibles. Cracking the insulator will make it worthless to collectors, as it's considered damaged. Collectors look for perfect examples in glass colors, other than clear or pale green, and unusual shapes.

2. Pre-heat your oven to 400 degrees. Place two of the insulators you want to crackle in an oven-safe metal pan. Once the oven reaches the correct temperature, place the pan of insulators inside and cook them for about 30 minutes.

3. Fill a gallon bucket about half full with cold water and a few ice cubes.

4. Turn off the oven. Remove the insulators from the oven with an oven mitt.

5. Plunge the insulators gently in the bucket of cold water. Do not drop them or they'll break. They'll crackle instantly, but leave them in the water to cool.

6. Remove the insulators from the water.

Tips & Warnings

• Experiment with the oven temperature and length of cooking if you want smaller or larger crackles.

References

• Collectors Weekly: An Interview With Antique Glass Insulator Collector Ian Macky
• Thrifty Fun: Making Crackle Glass for Crafts