Gemstone Coloration and Dyeing – Copper Series

Various and attractive shades of blue can be induced in gemstone by the use of copper compounds. This is perfectly logical, considering that several of our blue gemstone or mineral species owe their color to the presence of copper compounds. Familiar examples of these are malachite, chrysocolla, turquoise and azurite.

The Blues: Cobalt Series

1. Copper Nitrate

Materials needed:

  • Copper nitrate (cupric nitrate), Cu(N03)2 · 3H20

Procedure:

  1. This is a very simple process. Simply prepare a saturated solution of the copper nitrate in water, It is very soluble, so use the water sparingly. Pour the copper nitrate crystals into a glass jar and add warm water a little at a time while stirring (with a plastic or glass spoon or glass stirring rod). Add the water until the crystals are almost all dissolved. If all the crystals are not dissolved after several minutes of stirring, you probably have a saturated solution. If there are still undissolved crystals the next day after the solution has cooled, you can be sure of it. This process produces only rather light shades of blue even from a saturated solution, so if your solution is less than saturated it may produce a shade of blue lighter than you wish.
  2. Immerse thoroughly washed and dried slabs carefully into the solution. Store for at least two weeks. Pour of f the solution and save it. It can be used repeatedly, but if the surplus copper nitrate crystals at the bottom of the container disappear, add more so as to maintain saturated solution. Rinse and dry the slabs.
  3. The copper nitrate process produces good results on Mexican dendritic agate, white polka dot agate, troyite and snakeskin agate. The color can be intensified some if desired by heating the colored slabs in the oven at low heat (140° -150°F) for several hours. A “sand bath” is not needed.
  4. Preforms, baroques, etc., colored by the copper nitrate process tumble well. They actually seem to improve in hue during the tumbling process.

A disadvantage to the copper nitrate process is the tendency for the colored slabs or finished cabochons to develop a thin powdery white film over them after several months. This does no harm and is easily wiped of f but may cause some concern. Colored slabs or other pieces that have gone through the tumble polishing process do not develop this film. This suggests that if the colored slabs are soaked in water for two or three weeks, they will not develop this powdery white film. This is true. The following two processes which also use copper nitrate are much less conducive to this formation of film.

2. Copper Nitrate – Sodium Phosphate

Materials needed:

  • Copper nitrate (cupric nitrate), Cu(N03)2. 3H20
  • Sodium phosphate, Na2HPO4. H2O

Procedure:

  1. Soak slabs or other pieces in a saturated solution of copper nitrate, as with Process No. 1 above for the appropriate time. Slabs will need two or three weeks; thicker pieces will require proportionately more time. At the end of the soak period, drain of f the solution and save for re-use. Rinse and dry the slabs in the oven at lowest heat overnight or longer.
  2. Prepare a saturated solution of the sodium phosphate. Strength of solution is not critical but it should be strong. Immerse the slabs from procedure A in this second solution and store for at least three weeks. Drain of f the solution and save for re-use. Rinse and dry the slabs, and they are ready for use.

This copper nitrate-sodium phosphate process theoretically converts the copper nitrate in the slabs to copper phosphate. You may not agree that the coloration produced by this process is any improvement over that resulting from copper nitrate alone, but I think it is. It has seemed to me that, in snakeskin agate at least, the sodium phosphate soak imparts an additional translucency. Besides snakeskin, the process works well on coconut agate (variable), stinking water plume, Mexican dendritic, polka dot agate (white) and troyite.

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3. Copper Nitrate – Sodium Carbonate

Materials needed:

  • Copper nitrate (cupric nitrate), Cu(N03)2 · 3H20
  • Sodium carbonate, (Na2CO3), washing soda (laundry or household grade available at grocery stores is entirely adequate)

Procedure:

  1. For the first soak, proceed precisely as with the first soak in the preceding process. In fact the same batch of copper nitrate solution may be used for both processes and for any other process where copper nitrate is called for.
  2. Prepare a saturated solution of the washing soda. It is fairly soluble; sixteen tablespoons to a pint of warm water is sufficient. Immerse the slabs from procedure A in this solution for about four weeks after which time drain of f the solution and store for later re-use. Rinse and dry.

This process results in a little deeper shade of blue than does copper nitrate alone. I have obtained good results on snakeskin, Mexican dendritic, troyite and polka dot agate (white).

4. Copper Nitrate-Anunonium Carbonate

Materials needed:

  • Copper nitrate (cupric nitrate), Cu(N03)2 · 3H20
  • Ammonium carbonate, (NH4)2C03

Procedure:

  1. Soak slabs in saturated solution of copper nitrate as in the preceding three procedures.
  2. Prepare approximately a saturated solution of ammonium carbonate. Being very soluble, a pound will make only about one pint of concentrated aqueous solution. It can be used repeatedly providing a tight lid is kept on the container to keep the volatile ammonia from escaping. Soak the copper nitrate treated slabs from procedure A in this solution for at least four weeks. Drain off the solution; rinse and dry the slabs.

You will readily see that this copper nitrate-ammonium carbonate process produces a deeper blue than do the three preceding processes. It works well on snakeskin, Mexican dendritic, troyite and polka dot (white) agate.

5. Copper Chloride – Sodium Carbonate

Materials needed:

  • Copper chloride (cupric chloride), CuCl2 or CuCl2 · 2H20
  • Sodium carbonate, (Na2CO3), washing soda (laundry or household grade available at grocery stores is entirely adequate)

Procedure:

  1. Prepare approximately a saturated solution of the copper chloride. This salt is very soluble. It will require about two and one-half pounds of the salt to make a quart of the concentrated solution which can be re-used indefinitely if kept uncontaminated with other chemicals. Do not cover the container with a metal lid; it will corrode. Soak clean, dried slabs in this solution at least two weeks. Drain of f the solution, rinse the slabs thoroughly and dry. In this case, it is not advisable to dry the slabs in the oven after they have been soaked in copper chloride unless your oven can maintain a low heat of not over 125°F. Drying the slabs at higher temperatures tends to produce a brownish discoloration probably due to the formation of anhydrous copper chloride which is yellowish-brown. Theoretically, this discoloration should disappear during subsequent treatment, and while it usually does, in some processes it does not entirely.The saturated solution of copper chloride is a beautiful, deep green, and in most instances, so are the slabs that have been soaked in it. You will be tempted to go no further and to use the beautiful green slabs as is when they are taken from the copper chloride soak. However, you will be disappointed, for the slabs and any cabochons you would make from them will slowly lose this beautiful green color and turn bluish. This green can be otherwise produced or even enhanced in stable form, as will be discussed in a subsequent chapter, The Greens , under the copper nitrate-sodium nitrite process.
  2. Prepare a saturated solution of washing soda and proceed exactly as outlined in copper nitrate-sodium carbonate Process No. 3 above.

This process is so similar to no. 3 that you might expect the results to be similar. However, the copper chloride-sodium carbonate gives more of a greenish blue to snakeskin agate and some of the others than does the copper nitrate-sodium carbonate process. The present process works well with snakeskin agate, agatized bog, Mexican dendritic, polka dot (white) and troyite.

6. Copper Chloride – Aqua Ammonia

Materials needed:

  • Copper chloride (cupric chloride), CuCl2 or CuCl22H20
  • Household aqua ammonia as available at the grocery stores is entirely satisfactory.

Procedure:

  1. Prepare a saturated solution of copper chloride as prescribed for Process No. 5 above. If you have already prepared a solution of copper chloride for Process No. 5 or some other process, it can be used for this or any process calling for copper chloride. Soak clean, dried slabs in this solution for at least two weeks after which pour it off and store for reuse. Rinse the slabs well and dry in a tray (lowest possible oven heat) for several hours.
  2. Soak the slabs from procedure A in the aqua ammonia for four weeks in a jar with a tight lid. If common household aqua ammonia is used, do not dilute it. If commercial aqua ammonia (ammonium hydroxide) is used, dilute it one part of the ammonia with three parts water. This had best be done outdoors, because the fumes of the concentrated aqua ammonia are a powerful irritant to the eyes and mucous membranes. You may find even the diluted aqua ammonia objectionable indoors until you become accustomed to it. At the end of the soak period, pour of f the ammonia and store (tight lid!) for further use. It may be reused indefinitely or until it seems to be getting weak as indicated by lack of strong odor of ammonia. Be sure the container has a tight lid or the ammonia fumes will escape and gradually weaken the solution to the point where it is ineffective in imparting the desired blue.

The copper chloride – aqua ammonia process produces a beautiful sky blue on snakeskin agate and more or less lighter tones on most others. This process does not work well with granite, moon agate, Priday Ranch thundereggs and Wascoite.

Read also:

Gemstone Coloration and Dyeing – Table of Contents
Gemstone Coloration and Dyeing – The Blues: Cobalt Series
Gemstone Coloration and Dyeing – The Blues: Iron Process

By George W. Fischer
Copyright © George W. Fischer 1990
1961 Edition, published by Lapidary Journal. Inc. San Diego, California.
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