Coldworking

Lap Grinder

Before the surface is coldworked

After the surface is coldworked     

This week we have been working on coldworking techniques. Coldworking is what you do after hotwork, or glassblowing, in order to improve your work. Coldworking describes a great variety of processes in which glass is removed from the surface of an object with a scratching, grinding or chipping procedure. Using electrical equipment, such as grinders, laps, and wet belt sanders which are specifically made to work wet to avoid the glass catching on fire. For our coldworking process I used the Rotary Lap Grinder. These machines use Silicon Carbide coated or diamond discs to grind and polish glass. This machine also sprays a jet of water to the center of the disc so it spread all the way out as the disc rotates. Most machines use either a Velcro or magnetic hold to attach the diamond discs to make it easy to change from one grit to another. As I grinded the chandelier pieces we had made, I had to make sure the piece was evenly balanced the whole time on the wheel to ensure it was level  and flush, occasionally turning the piece 180 degrees so the disc hits all sides of the piece. I grind the glass in one direction, so all the scratches created by the grit are in the same direction. I then move on to the next stage while using another disc with a finer coarse grit, grinding the glass across the scratches. Here, the finer grit has removed the coarser grit grind. After we’ve achieved the smoothness we want, we go on to polish. We move to a softer pad and pour some Cerox mixture, a rare earth based powder, onto the disc. Cerox is suited for high production polishing where extremely bright finishes are required. Although you work only in one direction to grind, it is important to move the glass around as you polish. I also learned about beveling sharp edges, although this process wasn’t necessary for what needed to be done for the chandelier pieces. Being a ceramics major, I had a little understanding of how to bevel and what it did for the piece.  A sharp 90 degree edge is very fragile and prone to chipping. The bevel prevents chipping from trivial trauma and the bevel actually makes the edge look more finished and smoother. You’re not completely finished after you blow glass and place it in the annealer to cool down. Coldworking is essential for giving your piece a smooth touch and finished look before assembling.