How to Grind Glass and Apply Copper Foil

Arched Window with Stained Glass Border

Grinding takes cut pieces to their final shape. Foiling wraps the edges in copper tape so the pieces can be soldered together. Both are simple, but small mistakes show up in the finished solder lines, so it is worth being methodical.

Grinding

Setting up

  • Fill the water reservoir and keep the sponge in contact with the water so the bit stays wet. Wet grinding keeps the glass cool and stops dust becoming airborne.
  • Choose the bit: the larger one for general edges, the smaller for tight curves. A medium grit suits most glass. Fine grit is gentler on thin or fragile glass.
  • Wear safety glasses. Fingertip protectors or thin gloves protect against the ground edge.

Method

  1. Hold the piece flat and level against the bit. Tilting it upward causes chipping.
  2. Keep a firm grip. A loose hold makes the glass chatter against the bit.
  3. Let the bit do the work with light pressure. Pressing hard only heats the glass.
  4. Move the piece steadily along the bit and keep going until the edge is even.
  5. Check the piece against the pattern and grind until it fits.

Grinding is optional for leaded work, where the came forgives small differences, but it is useful for any piece that must fit tightly. Every edge should at least be safe to handle before it is foiled. Bits wear out when the grit wears bald, and a worn bit grinds unevenly and heats the glass, so replace it then. Empty and clean the water tray regularly.

Copper foiling

Choosing foil

Foil comes in widths from about 1/8 inch (3 mm) to 1/2 inch (13 mm). 7/32 inch (about 5.5 mm) and 1/4 inch (6 mm) are the usual starting sizes; narrower foil suits small pieces and wider foil suits thicker glass or bolder solder lines. Backings are copper, silver and black. Black-backed foil is used with dark patina, and silver backing keeps the line from looking coppery behind pale or transparent glass.

Method

  1. Clean each piece with a little isopropyl alcohol and let it dry. Any grease stops the adhesive gripping.
  2. Peel back a short length of foil backing and place the glass edge in the middle of the tape. The same amount should stand proud on the front and back.
  3. Begin away from a corner. Work around the piece and overlap the ends by a few millimetres.
  4. Fold the foil over onto both faces, finishing each corner with a small neat fold.
  5. Burnish the foil with a plastic fid or similar tool, pressing it flat on the edge and both faces.
  6. Trim any untidy edges with a craft knife.

Common faults

  • Foil will not stick. The glass is greasy or dusty, or the tape is old and the adhesive has dried.
  • Foil splits on inside curves. Warm it by working the fid over it first so it relaxes into the curve.
  • Foil lifts at the edges. Starting at a corner often causes this. Press it down firmly while burnishing.
  • Uneven solder lines. Usually the foil was not centred. Re-do it before soldering, because uneven foil shows.
  • Tarnished foil. Solder soon after foiling. If foil has darkened, a rinse in a mild vinegar and salt solution brightens it. Store unfinished pieces in a sealed bag.

When all the pieces are foiled, they are assembled on the bench and held with pins or a frame, then soldered.

In this section

Terms used here are explained in the Glass Glossary, and the Learn section covers the history and types of glass.