Q: Is there anything that will help a pickle solution remove those nasty pink oxide residues from the surface of jewelry?
A: This is a repost of Bill Sealy’s pickle formulae, which he has reverse-engineered from more toxic industrial techniques. The following formulas can be made up as needed, or they can be premixed and kept for an extended time in the original brown bottle that the hydrogen peroxide comes in. They can be reused until saturated (blue) or they stop working. Hydrogen peroxide decomposes rapidly when exposed to light, which is the reason for the brown bottle.
The active life of these pickles is limited to about four exposed hours, but you can extend the life of the solution by storing it in the brown bottles. Heat-treating and soldering of copper and copper based alloys can often coat the metals with a combination of black (cupric) and red (cuprous) oxide. The black oxide is easily removed in a standard warm sulfuric acid or Sparex bath. This will leave a red smut, which, with other undissolved oxides, forms a red oxide scale. This scale readily oxidizes further, leaving a dark, nonuniform patina. It can be imbedded in the metal during subsequent forging and drawing, so it should be removed. Abrasive removal of the oxides can result in loss of design details and crisp edges. This simple chemical treatment is offered as an alternate method for its removal.
Hydrogen peroxide (H2O2 ) pickle eliminates the need for abrasives, and has the added attraction of being relatively inoffensive. The following procedures and formulas provide for the removal of red scale from copper, brass, bronze, nickel silver, reticulation silver and some gold alloys. It will remove the copper coating from silver that has been accidentally pickled in an iron contaminated acid. Curiously, it will also remove the natural oxide layer found on aluminum. There is a great deal of latitude in the formulas and a variety of surface finishes and textures can be obtained.
It is suggested that you run some tests before applying these formulas to your work. Find the procedure that best fits your needs. When working with any acid the possibility of damaging your work always exists. These formulas can dissolve a brass piece and leave the silver solder seams standing. Hydrogen Peroxide pickle does not remove firescale from sterling silver. That oxide is black, not pink! Sorry! When there is a sulfuric acid component in these solutions it is already diluted with water to a standard pickle consistency of 5-10%. If you are starting with concentrated acid, remember: always add the acid to the water, not the other way around, and wear nitrile gloves and chemical-splash rated goggles. Household grade hydrogen peroxide comes from the pharmacy already diluted to 3%. The catalysts can be either measured or slowly added until bubbles begin to appear on a test sample of the metal. This signals that the solution is active.
SOLUTION #One (mild):
2 parts Hydrogen Peroxide (3%).
1 part water.
2-4% fresh sulfuric acid pickle (pre-diluted to5-10%) or Sparex solution.
SOLUTION #Two (strong):
½ cup Hydrogen Peroxide (3%).
1 Tablespoon fresh sulfuric acid pickle (pre-diluted to 5-10%) or Sparex solution.
STEP #1: Pre-pickle the piece in standard Sparex or sulfuric acid pickle solution and rinse well. These pickles work best when warm but not hot. All the black oxides should be removed in this step.
STEP #2: Place the Hydrogen Peroxide pickle container in a second bowl of hot water to keep it warm. If possible suspend the piece in the warm pickle or stir it gently with a feather or plastic rod . After a moment bubbles should appear on the piece. Agitate or brush with a feather to clear the bubbles. Remove the piece from the bath every couple of minutes to check the progress. It may take 5-10 minutes. Rinse well.
STEP #3: Use a stiff tooth brush or brass brush to remove residue and rinse.
STEP #4: Pickle again in standard Sparex or sulfuric acid solution (5-10%) to remove any remaining smut.
STEP #5: Repeat steps #2, #3 and #4 if necessary.
SOLUTION #Three: (For the faint of heart.)
3 parts Hydrogen Peroxide (3%).
1 part white vinegar (5%).
Follow the steps #1-3 listed for solutions #One and #Two. When the metal emerges from the pickle, it will be coated with a thick brownish green smut. Really ugly! This will flash off when dipped in undiluted white vinegar.
Notes: These solutions can also be applied to warm metal with a brush and worked into hard to get corners and intricate designs. Long term exposure to these pickles can cause the copper to be dissolved out of an alloy’s surface. Brass, for instance, can be pickled until it turns bright yellow. Even the mildest of the vinegar solutions can deeply etch if left unattended. A deep etch will often reveal the underlying crystal structure of the metal. Care should be taken and the process watched closely.
Bill Seeley MFA (Member-SNAG Reactive Metals Studio, Inc. / Corp. President PO Box 890 Clarkdale, AZ 86324, firstname.lastname@example.org) developed these formulae while studying for his jewelry MFA in the Department of Design at the University of Kansas. This is a repost of his information.