Liver of sulfur is a mixture of potassium sulfides which has traditionally been used to darken or ‘antique’ silver and bronzes. This involves a chemical reaction that oxidizes the metal surface and forms sulfide compounds. When you use liver of sulfur on these metals, the sulfur reacts with the surface and the atmosphere to produce the grays and blacks.
Editor’s note: oxidation doesn’t necessarily involve oxygen. The term describes a loss of electrons by a molecule, ion, or other atom during a chemical reaction. Oxygen was the first known “oxidizing” agent, reacting with iron to form rust, and remains the most important oxidizing agent on the Earth’s surface.
Usually a piece about the size of one’s little finger nail is dissolved in a cup or more of warm water. One may shake the jar it comes in to obtain small flakes which will dissolve quickly. In my opinion more dilute solutions give better control, repeated dippings and rinsing building up to the desired surface.
The fumes are dangerous and it should be used with good ventilation and covered right after use. It must not be allowed to come in contact with acids as a toxic gas is then rapidly evolved. It decomposes with exposure to light and air and so should be kept in a dark bottle that is sealed tightly. It is possible to keep for months if poured in hot. As the hot air contracts after sealing and cooling less air is available to decompose it inside the bottle.
To obtain black a number of repeated applications alternated with rinsing and brass brushing with a little soapy water is effective. A lustrous blue-black to steel gray may be produced on silver this way, and a purplish black on copper. Painting with the solution on specific areas accompanied by heating the object gently works well. An excellent black on sterling is obtained by sand blasting immediately before dipping into the solution. (don’t touch it with your fingers-any grease will interfere with an even coloring. This surface is fairly durable, particularly if gently brass brushed with some soapy water as a lubricant.
Liver of Sulfur does not take well on brass. Repeated heating and pickling or the introduction of iron to a pickle solution will coat the piece with copper which can be darkened. This is good for emphasizing recesses. This same idea is sometimes used on gold jewelry that has to be ‘antiqued’. Because gold alloys do not react to most sulfur solutions one can take some used pickle solution, place it into a bowl with the object and (wearing gloves) blot the object with some medium steel wool. This will contact plate the object and its recesses with copper. Then rinse, use the liver of sulfur solution to darken the plating to the desired level and buff off the surface with a rouge buff. The darkened recesses will be untouched by the buffing and so remain, everywhere else is bright.
Another way to work with it is to use rubber gloves and hold a small lump of liver of sulfur and draw on the metal surface with it while it is held at an angle under cold running water. This gives some interesting effects even on brass.
Liver of sulfur (potassium sulfide) powder is not the best way to obtain it. Lump form lasts longer. Light and air will destroy it so keep it shut and in the dark. Use gloves. Don’t mix it with or place it next to acids dry or when mixed up (no pickle in your objects if you are coloring them) as this can release hydrogen sulfide gas which is very bad for you. Use ventilation with it.
Most people tend to use too much and too strong. Only mix up, as much liquid solution as you need to just cover your object, more is wasteful. Put hot or warm water into a glass or Pyrex or corning ware container. I take my clean object, put it under running hot water (to raise its temperature so differential coloring does not occur on the areas to heat up first when placed in the solution), then dip it in the solution for a moment or two, take it out, rinse and repeat until the darkness you want is achieved. A brass brushing with soapy water as a lubricant in between rinsings will render a shiny, uniformly dark metallic surface. By going slowly you have a lot more choice in color, tone and surface qualities.
While it is usually used to obtain gray and black colors on silver and copper there are a number of intermediate interference colors formed, particularly if a weak solution is used. These include yellow, reddish brown, purple and blue. Some people add a small amount of household ammonia to the solution claiming it intensifies the lovely blue-green-red-purple interference colors one gets when using a dilute solution and slow approach. These pretty colors are not very stable over time because they continue to react with sulfur in the air and darken. You can sometimes ‘save’ them by spraying an appropriate lacquer over them. They may be retained if the surface is properly sealed. Acrylic resin is the recommended sealer for durability and resistance to darkening in light. Some jewelers lacquers also work. Envirotex® works very well for this. It is usually best in my opinion to continue darkening to the grays and darks which will last indefinitely.
For grays and blacks on silver one can also react the surface with sulfur compounds to form black silver sulfide. Plasticine (Plastilina) modeling clay for example contains some sulfur compounds and it can be used to create patterns of darkness where it has been stuck on in contact with the silver for some time.
Ammonium Sulfide (used as a garden spray) is supposed to work as an alternative to liver of sulfur. Egg yolks will work in a pinch.