Pickle: Cleaning up after Soldering

When you heat up your work for soldering and reach the temperature at which solder flows, you are also creating oxides on the surface of your metal that mar its appearance. In November, we dealt with removing a particularly tricky oxide called fire scale. Other surface oxides are easier to remove, and for these the jeweler can use an acid solution commonly called pickle, which will also remove the residue of flux at the same time. You can also remove these oxides by abrasion using files or abrasive paper, but using a pickle is more efficient.

The traditional pickle used to be a 5% to 10% solution of sulfuric acid, but because both the fumes and any splashes are hazardous to humans and anything else around, many jewelers now use a commercially prepared, dry, granular, sodium bisulfate compound, which is a safer substitute but should still be used with care. Probably the best known is Sparex #2(tm), though various supply companies also have their own house brands. There are also special compounds for nickel or German silver, and even a Sparex #l(tm) for iron or steel.

Another pickle compound that has recently been touted is citric acid. You can find this “anhydrous fine granular citric acid” in the canning section of grocery stores, or you can purchase larger quantities from commercial chemical companies. While this seems to be even less toxic than Sparex(tm), its disadvantages are that it must be used while quite hot, creating the potential for burns, and it works more slowly than Sparex(tm). Jewelers allover the country are still trying out citric acid, and final results are not yet available. Some swear by it, especially for its non-toxic aspect, but others have returned to using Sparex(tm).

How strong to make your pickle solution is a matter of personal choice. I usually start with about a quarter cup of Sparex(tm) in one pint of water. If your solution seems too strong or leaves etch marks on your metal, you can dilute the solution with water. As the pickle is used, it absorbs copper ions that reduce its ability to clean metal. You can tell when pickle is about at the end of its usefulness when its color turns dark blue-green from the absorbed copper. At that point, you can add more Sparex(tm).

All pickling solutions work best when heated to about 180°F. What’s the best way to warm them up? A number of commercial electric pickle pots are available that are designed specifically to keep the solution warm, but a crock pot also works well and is much less expensive. The home appliance manufacturer Rival makes a one-quart crock pot called a Crockette(tm), which is ideal for most jewelry use. Since the fumes from a pickling solution are corrosive, I have long failed to understand why the commercial pickle pots don’t have covers; all the cheaper home crock pots do come with covers, making them an even better choice. Of course, once you’ve used your crock pot for pickle, you should never use it for food preparation.

Other choices for a pickle pot, used on a gas or electric burner, include the traditional copper pan; a Pyrex(tm) or Corning(tm) ware dish, enamel ware, or a stainless steel pan. Do not use regular steel or iron containers for pickling since the ferrous metals will cause a catalytic reaction that will then copper- plate anything put into the container. For this same reason, you should always remove all steel pins or binding wire before placing pieces in the pickle; likewise, you should never use steel tongs or tweezers when removing items from the pickle. And any pickle container should be covered, both for safety and to prevent evaporation.

Copper tongs are the standard tool for retrieving items from the pickle; you can also use bamboo, wood, or plastic tongs or tweezers. There are also tweezers with plastic-coated tips, but you need to be careful not to submerge the non-coated part in the pickle. I keep a small Pyrex(tm) bowl filled with fresh water right next to my pickle pot and automatically dunk the item into the water when I take it out of the pickle. Some people use a solution of baking soda and water to help neutralize the acid, but this really isn’t necessary unless you’re using sulfuric acid or an exceptionally strong solution of Sparex(tm). But it is necessary to wash all traces of pickle off the piece before continuing to work on it.

Small parts such as findings or settings can easily get lost in the pickle pot, so a small container is handy to have when pickling such tiny items. A miniature plastic jar, drilled allover with minute (less than .040″ or 1mm) holes works well. Plastic caps from liquid laundry detergent bottles or paint spray cans or anything that’s about this size (2″ in diameter and 1 1/2″ ta3l) are easily accessible and free. Attach a copper wire handle to the cap or whatever you’re using, making it stand high enough so that it extends out of the pickle solution, and your small-parts basket is ready for use.

Removing a flat sheet from the pickle pot can also be a challenge. In fact, it’s almost impossible to grab a sheet with tongs or tweezers if it’s lying flat on the bottom of the pot. The best way to deal with this situation is to avoid it, which you can do by creating an uneven surface on the bottom of the pot, for example, by placing in it a small lump of metal, glass, plastic, or other material not affected by the pickle. This will leave the metal sheet slightly raised, giving you a spot to grasp with the tongs or tweezers.

Over time, the pickle solution becomes contaminated with metal oxides, flux, antifluxes such as yellow ochre, bits of heat-sink material, casting investment, and other stuff. You can easily clean all this particulate matter out of the pickle by pouring it through a paper coffee filter. For safety, do this while the pickle solution is cold, and do it in a sink in case of spills.

While it is never advisable just to throw very hot items into the pickle, some splashing is inevitable: dropping hot metal into liquid makes it hiss and spit. First, you should let things cool off a bit to minimize splashing, and then when you do put your items in, use the lid as a shield, held just above the pickle pot. You should also protect the area around the pickle pot with either an acid-proof material or one that is easily and cheaply replaced. And since this will be in the soldering area, you also want this shield to be nonflammable.

A simple three-fold screen of aluminum foil is one possibility. Make three brass rod or wood dowel frames about 9″ wide by 12″ high. Join them with binding wire so they will stand up but remain flexible, and cover them with heavy-duty aluminum foil, leaving a slot near the bottom of one panel through which you can fit the plug of the pickle pot. Don’t forget to protect the area under the pickle pot as well.

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