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Selecting The Right Foil: To begin you will need to determine what size and type of copper foil you will be using. Foil is available in a variety of widths ranging from 5/32" to 1/2". The most common width is 7/32", but you may find 1/4" width a little easier to wrap around your glass pieces as centering the glass on 1/4" foil is less critical.
It's also available in a variety of thicknesses from 1 to 1.5 millimeter. The 1mm foil is the thinnest which makes it the easiest to fold down, but it has a tendency to tear also. The 1.5 mm foil is thickest and works just the opposite. It is harder to fold down and it rarely tears. Deciding the thickness of foil to use is really a matter of preference. 1.5mm foil is recommended for beginners.
Foil is available with an assortment of colors: copper foil with a standard copper back, black back foil, silver back foil, and double sided silver foil. If you are using an opalescent glass the color of your foil isn't as important because the foil doesn't show through your glass. However, if you are using any glass that is transparent, it is best to use a foil that will match well with your patina. For black patina use black backed foil and for copper patina use standard copper foil. If you are not planning on using patina and keep the solder's natural silver color, then choose silver back foil or for even more coverage double sided silver foil.
Applying Copper Foil: Copper foiling is the process by which the fine edge of piece of glass is wrapped with a continuous strip of copper foil. Because solder will not stick to glass, foiling each piece establishes a surface on which the solder will adhere.
It is critical for the foil to be wrapped smoothly and evenly along the edge of each piece. If not, the solder won't lay evenly and solder seams may look awkward. Proper foiling affects the strength as well as the appearance of the finished piece.
To maintain the alignment of your glass pieces, only remove and foil one piece of your glass from your layout pattern at a time. Make sure all glass pieces are thoroughly clean and dry before foiling. You may want to clean the glass edges with rubbing alcohol to assure all oils or other residues have been removed. This allows the adhesive on the copper foil to adhere more effectively to the glass.
Take the copper foil and hold it between your first and middle fingers. The paper backing of the foil should be on top, the non-adhesive side of the foil should face down. Remove approximately 1"-2" of the paper backing from the foil. Holding the glass in your other hand, center and attach the foil to the edge of the glass. Do not begin on the corner of the piece. Keep the foil underneath the glass and look over the top of the glass to check the foil alignment. Be sure to keep the foil centered on the glass edge as you foil each piece. Once glass is centered on the foil strip, peel back the paper while rolling the glass away from you. When you reach the starting point, overlap the foil no more than approximately 1/4" and cut it with regular scissors.
Using thumb and forefinger, press the foil around the edges of the glass (crimping). Make sure that an equal width of foil is wrapped on each side of the glass and no part of the edge is without foil. If the foil is distributed unevenly between the two sides of the glass, you will have uneven solder lines, and the strength of your panel may be jeopardized. If this is the case, you must remove the foil and begin again.
After foiling each piece, use a fid to smooth the foil against the glass using moderate pressure (burnishing). Inspect the pieces, making sure the foil is flat against the glass. Do not rake back and forth across the foil when burnishing, as this may cause tearing. Also make sure the foil is adhered completely to the glass. Inspect the foil on both side of the glass piece. If you find any small tails that stick out where the beginning and end overlap, trim off the tail using an etching knife.
Caution: Don't leave pieces in a foiled stage for any extended period of time without soldering them. The foil will oxidize and will not accept solder.
TIP: The copper foil method requires a lot of hand/eye coordination. There are many tools available to make this job easier. Hand and bench top foilers help center the foil; fids and crimpers help adhere the foil to the glass; foil dispensers keep foil organized and prevent rolls from unraveling.