In an effort to become adept in the treatment of outdoor lead sculpture it was apparent that new skills were needed for structurally repairing and cosmetically correcting typical problems encountered when faced with lead sculptures which have been outdoors for a number of years.
Outdoor sculptures made of lead are not solid but are hollow within and are generally 3/8-1/2 inch in wall thickness. Damages that occur to lead sculpture outdoors are deformation and tearing due to leads soft character. Damage also occurs because the interior may have ferrous bars set into the interior of the castings. When these ferrous bars corrode, the swelling of the corrosion will deform the lead. Squirrels also take their toll on lead sculpture by chewing away lead until details are erased and all there is left are teeth marks.
Repairs have commonly used lead alloys such as solder to make repairs. Although soldering was sufficient from a structural standpoint it was not acceptable from an esthetic standpoint as the repaired area was visually apparent due to the color difference between solder and lead even after aging.
For the sake of better appearances it was necessary to go beyond the ability to use solder alloys as fillers or to use soldering techniques to make structural joins. Other non-metallic fillers, such as epoxy putty are lacking in strength, ductility or the ability to bond to lead in a satisfactory manner.
Inquiring of Virginia Naudé, an objects conservator and specialist in outdoor sculpture conservation about lead sculpture led to an introduction to Andrew Naylor of Shropshire, England. Andrew is a specialist in the repair of lead sculpture, using a technique commonly known in England as “lead burning.” Through discussion of conserving and making repairs to lead sculptures with Andrew Naylor it became obvious that assembling the tools and materials and developing the techniques to successfully burn lead in the United States would be a lone endeavor. The knowledge base in this country no longer existed in the arts and so inquiries were made in the commercial sector.
Fortunately, close to Oberlin, Ohio in Cleveland, Ohio, is a firm which specializes in what they call “homogenous lead bonding” or, in other words, “lead burning” (actuality welding of lead and lead alloys).
This firm constructs anodes for the plating industry using both CP (chemically pure) lead and 7% lead (lead with 7% antimony added for better working characteristics). The firm generously consented to allow me to observe and be trained by the craftsman having the longest experience in the workshop. Interestingly, his father had also been employed in the same workshop and had done substantially the same job in his lifetime.
Using a mixture of gasses, such as oxygen and acetylene, and employing a torch, is generally the technique employed to melt metal such as in oxy-acetylene welding. However the whole process for lead is more complicated.
In gas welding, oxygen and a flammable gas such as acetylene are needed to provide the hot flame to melt the metal and also in the process create an envelope of the gas mixture around the weld area as the weld progresses to keep out ambient oxygen, thus keeping the molten metal from oxidizing and burning away. Acetylene for use as the flammable gas is good for welding steel but has drawbacks in lead welding in that it can produce carbon in the form of soot which will contaminate the area where the lead weld is to take place thus keeping the molten metal within the weld from bonding. Also, acetylene is not as preferable as hydrogen when using tips with openings as small as .003 of an inch as required for fine joins.
Hydrogen is an extremely clean burning fuel, and although it does not produce as hot a flame as acetylene and oxygen, it is cleaner and more controllable in the miniature sizes of flame necessary for the work with lead.
However, no amount of specialized tools or gases will make lead bond together if the surfaces are not scrupulously clean. Various scrapers and files are used to remove soiling, oxidation and grease or oils from the surface. Most importantly, the scraped surface must not be touched after having being scraped. No rags nor even gloved hands; the last thing to touch the surface of the lead to be joined should be the scraper blade.
Scraper blades can be purchased such as the ones for woodworkers, but the most adaptable scrapers will be the ones that are custom made by the craftsman for the work in general, and then some specifically adapted for the task at hand.
The risk of ingesting lead dust or breathing lead fumes must be certainly avoided. To be safe, the following are required: a specific work area that can be cleaned and hosed down; clothing that if contaminated can be washed or properly disposed of; gloves to keep the greater amount of lead off the hands; and a properly fitted vapor mask with cartridges for lead dust and fumes. Cleanliness must be observed at all times. Absolutely no ingestion of food allowed and no smoking while in contact with lead. Thorough washing before eating is required.
The first step in the process of lead welding is to clean the surfaces of the pieces to be joined or the area to be filled by scraping, or coarse filing followed by scraping, until the surface of the metal is clean and bright. If the metal sculpture is of rolled sheet lead, either CP or 7%, it will be dense and uniform with no internal impurities. However, if the metal is a casting, as most lead sculptures are, the body of the metal is not compressed, the grain structure is larger, and the body of the casting may be like a sponge that will likely be full of impurities and gas pockets. These impurities must be eliminated if the welding is to be successful. After scraping and preparing the surface, the torch is used to prepare the metal prior to attempting any welding work. This preparation is accomplished by heating the metal with the fine tipped torch and creating a small puddle of molten metal which can be manipulated with the flame and movements of the torch. As the puddle is delicately manipulated, melting the lead to a depth of a few millimeters, impurities will rise to the surface of the puddle. With a little practice, these impurities can be popped off the surface of the molten puddle with the manipulation of the torch or by poking them off the puddle with the tip of a lead alloy filler metal rod. This preparation leaves good solid metal along the margins of the area needing repair. The next step is to once again scrape the surface to a bright finish in preparation for the filling weld. The scraping is necessary because no flux is used to protect the surface of the metal from oxidizing, and anything other than bright metal will form a skin that, when the area becomes molten, will contaminate the weld. Even the weld filler metal must be scraped bright.
All this is in preparation for the filling of a void or repairing of a crack. The work will proceed in the same manner as gas welding of steel but two major differences exist. One difference is that if the area of work gets too hot, it will just cave in, and all the hard work will be lost. To avoid this, the flame of the torch is tiny and tight and is manipulated in such a way as to bring it in and out of the weld area as work progresses. Secondly, it is hard to get the lead to flow and bridge gaps because it wants to form flat puddles and gravity makes it easiest to weld horizontally rather than vertically or overhead. So the piece being repaired is shifted and moved by the worker as the work progresses to take advantage of these naturally occurring tendencies.
The lead filler may be sculpted with the torch and filler rod to some extent depending on the skill of the operator. It is easier to take care of the sculpting as you go along rather than having a lot of excess lead to be removed by filing and grinding when you have completed the bond. Less fillings and avoiding making dust are important. Planning the weld repair and finishing with the filler as the work progresses is the most economical and safest way to work.