Materials and Equipment
- silver or gold alloy solder
- flux and flux brush
- fire bricks
- annealing pan
- tripod with rack
- soldering tweezers
- third hand
- solder pick
- steel straight pins
- steel T-pins
- iron binding wire
- yellow ochre or typewriter correction fluid
- acid (Sparex¨, sulfuric, or nitric)
- hot plate or crockpot
- compressed/air-natural gas or acetylene torch and tips
- striker and flints
- container of cold water
- sodium bicarbonate
Silver solders are alloys of fine silver, copper, and zinc. They are classified according to the temperature at which they melt -- IT, hard, medium, easy, and easy flo. These have melting points that range from 1150-1600°F and are used with metals with melting temperatures of 800°F or greater. Soft solders melt at temperatures below 800°F. Because the different grades of solder melt at different temperatures, multiple or sequential soldering on a single piece can be accomplished. When a series of soldering operations are anticipated on the same piece, the first seam is soldered using hard, the second seam is soldered using medium, and the third seam is soldered using easy.
grade flow point composition IT 1490 80 Ag / 16 Cu / 4Zn hard 1450 75 Ag / 22 Cu / 3Zn medium 1360 70 Ag / 20 Cu / 10Zn easy 1325 65 Ag / 20 Cu / 15Zn easy flo 1270 50 Ag / 16 Cu / 15Zn / 16Cd / 3 Ni
Solder is produced in wire and sheet. Each must be marked or coded to distinguish melting points. Solder wire or sheet must be cleaned with steel wool to remove oxidation and then handled carefully to avoid imparting oils. Solder is then snipped or cut into smaller pieces called "snippets" or "pallions." It is advisable to cut only the amount needed for each operation, as older "snippets" which go unused for extended periods may become oxidized. Accidental substitution of solder can be problematical, so always store cut solder in clearly marked, air-tight containers.
FluxSoldering requires flux -- a chemical agent containing borax -- to prevent oxidation of the solder and the metals being joined. If flux is not used, an oxide will form and prevent the solder from adhering to the surface of the metal. Flux containing borax becomes fluid at temperatures above 1100°F and are suited for use with solder that melts above 1100°F.
Solder InhibitantsWhen a piece of work requires more than one soldering operation, there is some danger that previously soldered seams will re-melt. Typewriter correction fluid or a paste of yellow ochre and water may be applied to existing solder seams to prevent them from flowing. When applying yellow ochre, be careful that they do not come in contact with liquid flux or "bleeding" may occur.
FittingAccurately file and sand the edges or surfaces of the pieces to be joined. A tight fit between the parts to be joined is crucial, as any gaps will create a condition unfavorable to the capillary action necessary for good solder flow. Silver solder will not fill gaps in a seam.
CleaningCleaning the metal prior to soldering is critical to successful soldering. Impurities (dirt, grease, oxidation, graphite, wax, etc.) hinder solder flow and capillary action. Metal may be cleaned with acid, abrasive paper, pumice and water, or detergent and water. After cleaning, handle the metal by the edges.
- Prepare the pieces of metal to be joined. They must fit accurately and be as clean as possible.
- Clean solder, snip into pallions, and flux to prevent oxidation.
- Position pieces to be soldered on a fire brick or other appropriate support. Pin pieces securely in place.
- Apply flux to all exposed surfaces.
- Position pallions of fluxed solder along the seam. Use only the amount necessary to fully flow the seam, as an excess of solder will require hours of clean-up.
- Allow the flux to dry.
- Light the torch and adjust to a low drying flame. Slowly move the flame over the surface to completely dry the flux.
- Turn torch up to a soldering flame. Pre-heat the entire piece by slowly and evenly moving the bushy tip of the outer flame across the surface of the metal. Continue general heating until the flux melts into a clear liquid.
Use the flux as a temperature indicator. Borax-based flux turns chalky in the initial stages of heating. When the metal approaches soldering temperature, the flux will melt, turning brown and then clear and "glassy." Too much heat or too little heat applied for an extended length of time, causes the flux to "burn out" and lose its oxide-absorbing property.
- Continue to move the flame, but concentrate the heat in the area of the seam.
Solder will flow toward the hottest point, so even flow depends upon all pieces being the same temperature. Smaller and thinner pieces will heat more quickly, so direct the heat to the larger or thicker pieces to be joined.
Do not concentrate the heat on the solder as it will melt but not flow. As the entire area equalizes at the solder's melting point, the solder will flow.
If a "snippet" of solder needs to be repositioned during soldering, use the solder pick to reposition it. Dip the pick into a bowl of cold water first so that the snippet doesn't stick to the pick.Repositioning is easiest after the flux has melted and become sticky.
- As the solder begins to melt it will flow toward the juncture of the pieces to be joined through capillary action. Once the solder has begun to flow, keep the heat steady and even as it will "freeze" if the heat is removed, or concentrate in hot spots.
It is possible at this point to lead or pull the solder along the seam by creating a moving hot spot.
If the fit of the pieces is good, and the heat has been applied correctly, the solder will flow into the joint forming a thin seam which will be nearly invisible once the piece is cleaned and sanded.
- Air cool the piece completely. Do not quench the soldered piece as this will warp the metal and weaken the seam.
- Clean the piece in warm acid to remove flux and oxidation.
- Rinse well and dry.
- Lead solders are not allowed in the studio. Lead based solders should never come in contact with metal that will be silver soldered.
- Remove solder inhibitants with water and a toothbrush before cleaning in the acid.
- Iron and steel tools (pliers and tweezers) should not be used to place or remove work from the acid. Use only copper, or plastic tongs. Iron bearing tools will contaminate the acid causing pieces to become copper plated.
- Straight pins, T-pins, and iron binding wire must be removed before cleaning pieces in the acid.
- Care must be taken to never completely enclose a hollow construction unless vent holes have been drilled. Without venting, a hollow constructed form may explode.
- Use proper ventilation. Many commercial fluxes contain fluorides which will produce a gas which irritates eyes and nasal passages.
- Take care when placing pieces to be cleaned in the acid. Hold the lid of the acid bath between you and the acid to protect skin and clothing from splashes. Clean up acid spills and splatters by neutralizing them with sodium bicarbonate. When preparing acid baths, always add acid to water to prevent an explosion from concentrated acid.
- Never leave paper towel waste in the soldering area