Double is a German word of french origin meaning rolled gold or gold fill material. I use it for the gold-fill material described here to differentiate it from the commercially produced sheet.
Hand made double has different qualities than the manufactured metal. It is far less perfect, its finished size is limited by one’s workshop facilities and counting hours it costs more per square centimeter. Control over metal thickness while making is enormous and it may be made many hundreds of times thicker than the manufactured sheet. One has control over the metal used and so one can use 24K gold which is not done commercially as it is too soft for general use. Because one is making it from scratch there are many opportunities for decision making for aesthetic reasons which do not exist when one uses the manufactured material. Also, in North America commercial production of sterling double (or gold fill) is very limited and there are large minimum order requirements.
Prior to 1978 I used fire gilding (mercury amalgam gilding) fairly often in my work. Various gilding and gold overlay techniques interested me. 1979 brought me to Pforzheim, West Germany where I studied under Klaus Ullrich at the Fachhochscule fur Gestaltung. In the 1960’s he had done a great deal of fusing of 18, 22 and 24 karat golds in his work. As the gold price climbed he had begun making double material in order to retain the pure gold color on his work and still keep the work’s price down somewhat. I visited his workshop and watched him fuse a sheet of .3 mm 24K gold to a 1 mm sheet of sterling silver. He used a large propane/air blowtorch with the air supplied by a foot bellows. This he rolled out to the size he needed, controlling its shape by directional rolling. The final roll was done with paper printing the gold to break up the light reflecting from its surface.
When I returned to Canada in 1980 and set up my own workshop I began to experiment with this fusing technique in order to have the pure 24K color, the strength of sterling and not spend a fortune on inventory. Ordinary torches did not work well. Acetylene proved too hot and concentrated and propane/air too oxidizing. Finally I used a mouth blowpipe with propane gas. This allowed me tremendous control of the gas and the air ratios and over the areas of high heat while fusing. Fusing is performed on charcoal to eliminate oxygen and a highly reducing flame is used for the same reason.
While I began by using .3 mm gold sheet, 1 mm sterling and flux to fuse with as I understood the process more I went to .1 mm gold sheet and 1.5 to 2 mm silver with no flux, just using the reducing atmosphere of the flame and charcoal. Because the heat produced depends on how much oxygen you supply with your lungs the process is very direct and can be done slowly enough to ensure that the two metals do not completely alloy together but just join. At first I used it as a way of obtaining plain gold surfaces. Then it became obvious that like Mokume one could engrave through the surface exposing the silver underneath and use this to graphic advantage. By engraving before rolling one could determine the width of lines by the direction in which they were rolled. Line width, texture and relief is also controllable by re-fusing at later points. I was able to draw with the metal as if it was paper.
In the industry the fusing procedure is similar to the way in which Mokume is made. An example I saw in Pforzheim was a sheet of gold 1 mm thick, 10 x 30 cm in size, scrupulously cleaned and placed over an equally clean slab of sterling, 10 x 30 x 10 cm thick. The gold alloy most often used is a 14 karat one with slightly more silver than copper chosen for its long wearing properties. Two steel plates (10 x 30 x 2 cm thick) were placed over and under the gold and silver. The whole thing was wrapped in brass foil like a package and folded tightly closed. This excluded oxygen. It was put in a gas kiln (a controllable atmosphere; probably reducing) for 6 or more hours until it reached the correct temperature when it was taken out and swiftly placed under a drop press which slammed down on it. After this the bonded slab was unwrapped and rolled out or stamped to form sheet, tube and so on.
Although an acetylene torch could be used given enough practice and a small enough blank to be fused the best flame, as said, is a soft, not too hot, splashy, reducing flame over charcoal. This allows good control and also gives time to see hat is happening and to make decisions while fusing. My blowpipe costs about $15.00 and is available from European tool companies. I sawed off the tip from a “Bernz-o-matic” ® type small propane torch kit and clamped a rubber hose to the brass tube that was left to supply the blowpipe with gas. The oxygen comes from my mouth in a second tube. The most difficult part of using a blowpipe is that the flow of air must never stop. This means that, like a horn player, one must breathe in while a reservoir of air held in the cheek supplies the torch. This is replenished as one breathes in and so the flame is never interrupted. Facility with this is best accomplished by practicing with one of the old-fashioned smaller blow-pipes used with an alcohol lamp. Alternatively one can use bellows or learn to do it with a sharper, hotter flame. A natural gas/air torch would work quite well.
While 14 karat, 18 karat gold etc. may be used, 24 karat gold offers the best chance for success as its melting point is so far above that of sterling that it does not alloy throughout easily. This means that where alloying takes place during fusing it is usually over the surface of the gold sheet only and can be scraped off or emeried off regaining a gold surface at the point where it occurred.
The gold may be fused to fine silver or sterling. Sterling works well but oxidation may present a problem which fine silver avoids. Fine silver of course is too soft for any load bearing part of a construction. Gold may also be fused to copper but this is extremely difficult as the copper-gold alloy formed melts at a relatively low temperature and spreads very rapidly through the fold, not just over the surface. It is possible to use this effect with copper to create areas of varying alloy content (rose gold to red gold) on the copper surface and then bring out their colors by suitable chemical treatment.
24 karat gold is extremely soft and double made with it is very liable to damage. Even a fingernail can scratch a rolled paper finish on it. Therefore a 24K double surface should be protected from abrasion by surrounding walls and by function, that is it is not suitable for rings or bracelets but is best for pins, earrings and small sculptures. If one burnishes the surface then it won’t be effectively damaged by further abuse. One can also use a hard gold alloy for the double material.
What follows is small scale double making procedures with limited equipment
1. Roll the gold out to between .3 mm and .1 mm thickness on clean rollers. Anneal the gold when it shows signs of curling and increase the pressure in small increments to avoid rippling of the sheet. One can roll it incredibly thin on one annealing but ripples and edge cracks may result. Keep it as flat as possible. If it is not completely flat leave it curved rather than damaging the smooth rolled surface by malleting which may cause air to be trapped in the texture formed while fusing. It can if necessary be flattened when hot while fusing.
2. The silver used should be at least 1 mm thick and thicker metal will give greater surface area of gold for the same original starting area and end thickness. The thinner the final layer of gold the greater the degree to which the silver alloy approaches its surface. With very thin layers the gold becomes paler and greenish. Less than .1 mm gold to 2 mm silver will run the danger of alloying through and becoming part of the silver blank while fusing or just losing color intensity on the final piece. Because the silver also comes through the gold layer to some extent on very thing gold layers oxidation can take place leading to a spotty or speckled effect, this after rolling of course.
3. The silver is cut to the required blank shape for fusing. Rounded or oval shapes are best for least stressful rolling but square and rectangular ones work well. The final material may be cut to any shape and soldered on or into other metals. With freeform shapes with re-entrant angles tearing of the blank while rolling is almost certain to happen unless great care is taken.
4. The silver blank is placed on the gold sheet and the gold cut out around it with shears or scissors leaving about 1.5 – 2 mm extra gold around the silver. This is to prevent any silver alloy formed while fusing from crawling over on to the top surface of the gold sheet.
5. Both gold and silver are now cleaned on their contact surfaces. A medium or fine emery mandrel on the flexible shaft works well. One may scrape the silver clean but scraping the gold sheet will cause it to curl up. Do not touch cleaned surfaces with the fingers. Place the cleaned surfaces together.
6. There are two possibilities at this point. One may fuse the sheets together or fix the sheets in position and then fuse them together. To fix them one takes a piece of leather or folded paper towel and puts the gold side down on the leather. This is then rolled with a fairly light pressure. This forces the gold to form itself around the sides of the silver blank and fixes it in position. This prevents the gold sliding off when fusing as can sometimes happen. It also makes sure that contact between the gold and silver sheets is very close indeed. It tends to prevent oxidation of the contact surfaces.
There are problems with this method as air may be trapped under the gold sheet if the sides fuse first and more importantly one cannot see the temperature or surface texture of the silver as it heats, nor can one see the ‘flash’ of silver alloy that seals the gold to the silver. One can overheat because of this and cause the silver alloy to come through the gold sheet. Unless one is practiced it is easier and more controllable to simply fuse the flat gold to the silver and not to bother forming the gold around it.
7. The fusing is done on a new or flat-filed charcoal block with at least 2 cm charcoal on each side of the blank. As the charcoal burns it uses up oxygen. The gold sheet is placed on the silver (clean sides in contact) if it was not pressed over it. A very bushy gas rich flame is used which envelops the metal and charcoal.
This flame is maintained and the temperature is slowly and evenly raised until the silver begins to near its melting point. If one is using gold pressed over silver care must be exercised at this point as the silver surface is mostly hidden from view and the silver alloy may unexpectedly appear through the gold. If one has placed the gold sheet on the silver it may be advantageous to have domed it slightly so that the centers of the sheets contact each other. If a reducing atmosphere has been maintained the centers which touch fuse first and the fused area moves outwards from there ending at the edges. If done properly this method eliminates air bubbles trapped under the gold. The moment that fusing has taken place; that the ‘flash’ of liquid silver alloy has been observed along the edges one should stop heating.
8. The double slug is quenched and checked for gaps at the edges. If any exist it must be re-fused to seal them. If bubbles show on the gold they may be burnished down with a fingernail. If large areas have not fused or large bubbles exist they must be pricked through, flattened and re-fused to the point that silver alloy is noticed at the prick mark.
9. Excess gold is cut off the slug and saved. Its sides are filed smooth and emeried as any indentations may become the origin of a crack while rolling. Because of the high temperature the silver is taken to its grain structure is not the best for rolling and every care must be taken to avoid damage to the sheet. After filing and emerying the back edge is beveled lightly with file and emery, again to avoid cracking.
10. The slug may then be rolled directly if a plain gold surface is wanted or if engraved lines having a sharper or finer look are to be put in at a later stage of rolling.
11. Otherwise one may mount the slug on a pitch stick or engraver’s ball for engraving, drilling, etc. If desired scattered silver filings could be fused to the gold surface beforehand for a dusted effect.
12. The slug is now engraved. Lines will widen in the directions in which most rolling takes place and this should be planned for as should the initial starting shape to prevent metal waste. A thin line however will probably remain relatively thin. A fine pointed center punch which pricks the gold surface will produce dots of silver on the final piece. On thinner gold heavily scribed lines will show up later also.
13. The slug is removed from the pitch, cleaned and rolled. When rolling increase the pressure in small increments and maintain your shape by constant directional rolling. At every pass through the rolls the edges should be examined for cracks. If even a tiny crack appears the edge at that point should be filed back just past the origin of the crack and the metal annealed. Even with larger cracks more metal is saved on the finished sheet by drastic surgery earlier on than would be if one let the crack go and tried to prevent it spreading. If a large crack occurs it can be hard soldered. This will show on the gold front as a line even with no solder spillage. The sheet should be annealed about every three passes through the mill. It is better to be too careful than to lose a sheet to cracks. If you hear it ‘tinkling’ then it definitely needs annealing.
14. When it is about the right thickness for your needs (I use .5 mm usually) one can choose to print the surface with a texture such as cloth, papers of different types and so on. One may also leave it shiny from the rolling mill and burnish the surface which protects it against damage.
15. The material is now finished and may be cut up and soldered to other metals or constructions to suit.
16. One can at this point (and earlier) widen lines selectively or cause them to bubble by careful re-fusing. This provides the possibility for further aesthetic choices. If one domes the double sheet and then, supported over air, gently brings it near fusing point the gold covered areas will sag leaving the silver lines as raised relief areas. This can be quite useful and provides some subtle height variations in the work. The relief can be quite high.
Careful re-fusing also seems to bring some silver through the gold allowing for the development of reds and oranges when oxidizing the double surface.
17. The finished piece may now be colored with liver of sulfur and ammonia. My experience is that most control is achieved in this case by using an alcohol lamp to heat the object with. This provides more or less heat as one needs. One begins by pouring some ammonia into a small container (household clear ammonia is best) and then painting the ammonia on. Keeping the metal surface moist the whole time is important. A tiny amount of weak liver of sulfur solution is introduced to the ammonia and this is painted on the same way. The color begins to develop slowly, first oranges, reds and so on. If it has gone too fast or is unsatisfactory one can anneal, pickle and start over. It is also possible to heat the double surface until the oxidation begins to disappear and then plunge it in to liver of sulfur solution which can produce a ‘solarized’ look to the areas around the exposed silver. The pin shown in the post card dated 1984 is an example of this. Exposed silver areas will turn black as is usual with liver of sulfur. The surfaces could be waxed slightly or otherwise sealed. I leave my surfaces unsealed.
There does not seem to be much of a problem with color fading. One silver piece I have oxidized yellow/purple/red is still unchanged after eight years without protection. This could vary with the surrounding atmosphere. As a final touch lines may be emphasized on a paper rolled finish by lightly burnishing them.
Double Making Steps
- Roll gold to desired thickness (.3 – .1 mm).
- Cut silver blank (1 – 2 mm thick).
- Cut gold out around silver leaving 1 – 2 mm outside silver edge.
- Fuse sheets together, on charcoal in reducing atmosphere.
- Quench, check for gaps in fusing, re-fuse if necessary.
- Clean up sides and edges of slug; file, emery to prevent cracks.
- Engrave slug if desired.
- Roll, keeping shape by directional rolling. Check constantly for cracks and repair as necessary. Anneal often.
- Roller print if desired.
- Incorporate into pieces.
- Color with liver of sulfur and ammonia.
Karl Fischer (Has English catalogue with prices)
J. Schmalz (Good catalogue, no prices)