Chemically Induced Inclusions – Copper Inclusions

This article is an excerpt from the book “Gemstone Coloration and Dyeing“, written by George W. Fischer, and discusses copper inclusions from the section ” Chemically Induced Inclusions”.

Since the original discovery described here, that the principle of electrochemical displacement of metals can be used effectively and easily to induce inclusions in snakeskin agate, I have tried the method on several of the other gemstone varieties described in this book and have found that some respond with interesting and pleasing results. These are coconut agate, Brazil carnelian and troyite. Besides these, several other agates have responded well to the process: umbu (a Uruguayan agate), Beacon Hill thundereggs (Idaho) and Thistle Creek nodules (Oregon). There is considerably more behind this method of inducing copper inclusions than merely the initial discovery. Many problems were encountered in developing the discovery into stable processes with consistently predictable results. Several variations of the basic process have been developed through the ensuing years and these are presented herein.

Copper Displacement: The Basic Process

Materials needed:

  • Copper chloride (cupric chloride), CuCl2 . 2H20
  • Iron metal (soft iron wire, 14-20 gauge)
  • Washing soda (sodium carbonate), Na2CO3


  1. Prepare a saturated solution of the copper chloride as directed under process No. 5. Soak clean, dried slabs in this solution for two weeks or longer. Pour of f the solution, and store for re-use. Rinse lightly and allow the slabs to dry at room temperature or wipe dry with paper toweling. The slabs should be more or less a rich emerald green; if they are pale green the probabilities of successfully inducing inclusions are much reduced. This does not apply to agate that already has some native color (e.g. Brazil carnelian), where the “rich green” may be partially obscured and not look so rich.It is advisable to leave the slabs in the copper chloride soak until you intend to start procedure B. In other words the slabs should not be allowed to dry except for the surface for the reason that if the slabs dry to any depth at all, the pores are no longer filled with a solution of copper chloride and displacement will not take place. Hence, no inclusions will result.
  2. Cut off a piece of the wire to convenient handling length, about ten inches, and more or less straighten it. Pull the wire through folded sandpaper until it is clean and shiny. With wire snipers, cut the wire into small pieces. One-eighth to one-sixteenth inch is a convenient size. Pour a little of the copper chloride solution into a small glass. Now arrange before you on the table where you are working the copper chloride slabs from procedure A, the small bits of iron wire and the small glass of copper chloride solution.Lay one of the slabs on a piece of paper toweling before you. With a pair of tweezers or better, small sharp pointed forceps, pick up one of the bits of wire, touch it to, or barely dip it into copper chloride solution. Place it on the slabs in the area where you want the inclusions to develop. Experience will teach you how many snipped pieces of wire to put on one slab. It will mostly depend on the size of the slab, the nature of the agate being used, etc. However, it must be remembered that these inclusions need space in which to grow and express individuality, and if too many are started on a given slab (i.e. too close together), they will become confluent and quite possibly less attractive this way. For example, on a slabs of snakeskin agate approximately two by three inches, I like to start a single colony of inclusions (usually moss or plume), so I place only one piece of dipped wire on it in the center. This gives plenty of room for the copper inclusions to develop and radiate out from the center, and frequently it is from the radiating periphery of the colony that the best inclusions develop. Lay the “inoculated” slab off to one side out of the way, and proceed similarly with the remaining slabs. [1] Should you not wish to use all of the copper chloride slabs at one time, return those not inoculated to the copper chloride soak until you wish to use them.Leave the inoculated slabs undisturbed in the open air overnight or for several hours at least. By this time, the copper chloride solution around each piece of iron wire will have dried and the pieces will adhere to the slabs.
  3. Prepare a saturated solution of the washing soda as prescribed for Process No. 5. After the inoculated slabs from procedure B have dried overnight, it is time to immerse them in the soda solution. Shallow plastic trays two or three inches deep are good for this. Pour the soda solution into the tray, to a depth of about half an inch. Immerse the inoculated slabs in the soda solution carefully and gently so as not to dislodge any of the pieces of wire. If one is accidentally dislodged, dry the area and reinoculate it.On some slabs and/or on some kinds of agate or other gemstone, the inclusions will begin to develop very soon. In fact, on slabs heavily charged with copper chloride (i.e. with a good green color), they may begin to show around the wire bits even before the slabs are immersed in the soda solution. The rapidity of growth of the inclusions, be they dendrites, moss, plume or all three, varies considerably among different kinds of agate and sometimes among different slabs of the same kind of agate. Occasionally, such variation will occur on the same slab of a given kind of agate. Probably this variation is a reflection of physical variation in the porosity of the agate.Keep the slabs immersed in the soda solution for about two weeks, more or less. The water will evaporate from the trays, causing the soda to crystalize out. As soon as this begins to happen, add a little water from time to time to replace that lost by evaporation. Inspect the slabs daily during the first ten days or so. If any of the rapidly developing inclusions are getting too large, remove the slab and allow it to dry on a tray. The individual slabs need not be kept in washing soda for four weeks. In fact, it is my own practice after the first week or ten days to keep only the rapidly developing slabs in the trays, the better to terminate the growth of the inclusions when this is desirable. The slower ones I put gently in a plastic container (a small waste basket) of washing soda solution and forget about them for the remaining time. It does not harm for the slabs to “pile up” in the solution in such a container provided they are handled gently so as to not dislodge any of the wire pieces. As soon as this happens, the growth of the inclusions beneath comes to a sudden, screeching halt.At the end of the four weeks, the slabs may be removed from the washing soda solution. Slabs with underdeveloped colonies of inclusions can be returned to the solution provided the wire bits are still attached. The others can be terminated simply by removing the bits of wire. Clean, rinse and dry the slabs. They are ready for use.You will observe that there is considerable variation in the nature of the copper inclusions that can be induced in different kinds of agate and to some extent even among different slabs of the same kind of agate just as there is similar variation in rapidity of growth of these inclusions. Of the several varieties of gemstone in which I have been able to induce inclusions by the copper chloride process, probably my favorite is the snakeskin agate. Not only do nice coppery and mossy inclusions develop in this agate, but the contrast they present with the bluish-green of the agate itself (from the copper chloride – sodium carbonate from Process No. 28) is beautiful, especially in the finished cabochons (Plate 9.10 ).In banded or fortification agate, the inclusions tend to follow the fortification layers yielding chevrons and other designs. Examples of this may be found in coconut agate, Brazil carnelian and umbu agate from Southern Brazil . However, there is considerable variation within each of the induced inclusions as well as the rapidity of growth. Often the inclusions are plumy growths of copper in the agate; sometimes beautiful, delicate dendrites are formed.Slabs from an occasional nodule will not yield any inclusions simply because they are not sufficiently porous to absorb enough of the copper chloride solution. In general, any time a slab does not absorb enough of the copper chloride to appear at least pale green, it is not likely to respond with inclusions ( Brazil carnelian excepted).

    The response of white polka dot agate and especially troyite is worthy of comment. On these opaque gemstones elaborate and extensive dendritic inclusions develop. Due to the opacity of these gemstones, the induced inclusions are scarcely apparent from the surface, but when cabochons are made from the treated agate, they are fully apparent. The finished cabochons are striking and suggestive of “porcelains”.

    Slabs that fail to develop inclusions will often do so “the second time around”, i.e., from a second soaking. Simply scrape of f the wire bits, wash the slabs and resoak in the copper chloride solution as before. I have even had instances where the recalcitrant slabs would finally respond after a third attempt. If a second or even a third attempt fails, I recommend that the slabs be soaked in aqua ammonia as in Process No. 6. The slabs may thus become a nice pale blue and can be used for cabochons, tumbling, etc.

    If you prefer you can use slender rubber bands to hold the bits of wire in place. This used to be my own practice until I learned that, as the displacement process progresses, the displacent bits of metal will adhere reasonably well of their own accord. If you do wish to use rubber bands, use small sizes so that they can easily be criss-crossed over the surface of the slabs. Simply raise a portion of the rubber bank where you want the inclusions to develop, touch a bit of the wire to the copper chloride solution, place it under the rubber band and then allow the rubber band to go back in position, thus holding the bit of wire in place. The rest of the procedure is the same as without the rubber bands.

    Not infrequently, the development of inclusions is accompanied by fracturing. The deposition of copper in the pores of the gemstone creates terrific pressure within, and sometimes this pressure is released via cracking, much like water freezing in a metal pipe and bursting it. This fracturing under pressure is seldom serious however. I do not recall ever having a cabochon break from these fractures, and they usually are not conspicuous in the finished cabochon. Furthermore, the nature and pattern of these fractures sometimes actually adds to the appearance of the cabochons, especially if the fractures are used as avenues for the impregnation of supplemental and complementary chemical coloration as will be described below.

Copper Inclusions – “Ghosts “

If the copper inclusions, as described in Process No. 36 do not develop in the proper medium (e.g. sodium carbonate) or are otherwise improperly cared for (especially after growth of the inclusions is terminated), the inclusions will more or less disappear leaving whitish areas in their place. These I call “ghosts”. Actually these “ghosts” consist of minute air spaces in the agate where the copper inclusions were. What happens to the inclusions? Where does the copper go? Actually, I can not explain their disappearances. They seem simply to be reabsorbed into the copper chloride impregnated agate whence they came. I do know that the gradual disappearance of the inclusions leaving “ghosts” in their place was a major frustration until I finally discovered how to fix them and make them permanent. This is the purpose of the sodium carbonate solution. It is an ideal medium f or the inclusions while they are growing and renders certain changes in the copper chloride slabs so that the induced inclusions are fixed and permanent after growth has been terminated.

While it was frustrating indeed to have beautiful inclusions disappear, this ill wind can not be said to have blown no good. Subsequent treatment of the slabs or cabochons with the “ghosts” has yielded some interesting and pleasing results.

If slabs or cabochons with “ghosts” are soaked in aqua ammonia a la Process No. 6, the agate itself will turn a beautiful sky blue accentuating the whitish “ghosts” in very attractive contrast. The opinion has been expressed to me by some that these “ghosts” thus dressed in blue are as attractive as the copper inclusions that caused them.

“Ghosts” rather than inclusions can be made simply by mistreating the developing inclusions, causing them to more or less disappear. Instead of using soda solution as the bath in which the inoculated slabs are incubated, simply use water with a very little detergent added. The inclusions will develop just as well as in borax solution, but they will not stay. After the inclusions have developed to the desired point in the water bath, remove the displacent bits of wire, rinse and store the slabs. After a few weeks, more or less, the inclusions will gradually disappear and be replaced by “ghosts” of the inclusions.

Ghost slabs and cabochons may be treated in other ways to improve their appearance. One such way is to soak them in sodium nitrite as in Process No. 30, procedure B. By this treatment the slabs become more or less an emerald green with the “ghosts” lighter.

Copper Inclusions – Complementary Coloration

Depending on the gemstone used for the purpose, the process for inducing copper inclusions imparts various shades of blue to the gemstone itself. While in some gemstone (e.g. snakeskin agate), the background color for the inclusions is attractive as is; still there are a few ways to modify this if variation is desired. These methods are the results of may experiments using various chemicals that had at least theoretical possibilities of enhancing the color of the copper included gemstone without disturbing the inclusions themselves.

A. Sodium Nitrite Treatment

As you will recognize this process is an adaptation of process No. 30, and changes the blue of the copper included agate to more or less of an emerald green, varying with the nature of the agate itself.

Refer to Process No. 36. Select out whatever slabs with developing inclusions that you wish to subject to this sodium nitrite process, leaving the displacent metal (the wire bits) attached. The selection should be made on the basis of the stage of development of the inclusions. They should have developed almost to the extent that you wish them to. They will continue to develop some after they have been placed in sodium nitrite solution. Prepare a strong solution of sodium nitrite, as called for under Process No. 30, procedure B, or the same solution can be used if you have it.

Immerse the slabs with their developing inclusions in the sodium nitrite solution taking care not to dislodge the bits of iron . Leave the slabs undisturbed in this solution for three weeks, if you can wait that long, after which, pour off the solution, and store for re-use. Remove the wire bits, clean up the slabs, and they are ready for use.

On snakeskin agate, this process leaves the inclusions with a nice green background. Whether this is better than the blue is a matter of opinion. I think they are both good. On other agate, like coconut, umbu and others that absorb less of the copper chloride than snakeskin agate does, the resulting green is paler and somewhat dusky.

B. Aqua Ammonia Treatment

This process also borrows from one presented earlier in this book, Process No. 6. The normal aquamarine blue of the agate that results from the copper chloride and sodium carbonate solutions in Process No. 36 is deepened both in hue and intensity. The intensity depends on how much copper chloride the agate had absorbed.

The procedure is much like that for Process No. 38A, but there is one difference. While the inclusions will continue to develop somewhat in 38A, in this process, they rarely do. So select slabs accordingly. Be sure the inclusions have developed as far as your wish them to go. And be sure the bits of wire are not dislodged.

Prepare a solution of aqua ammonia, as prescribed for procedure B of Process No. 6, or use the same solution if you already have it at hand. Immerse the slabs with inclusions in this aqua ammonia solution carefully, so as not to dislodge any of the wire bits, and allow them to soak for at least four weeks. Be sure the wire bits are not disturbed else the inclusions are apt to disappear and leave ghosts. At the conclusion of the soak, pour of f the solution and store in tight container for re-use. Remove the bits of wire, clean up the slabs, and they are ready for use.

This process gives the best results, in my opinion, with those agate varieties that are only lightly colored as a results of the prior bath in copper chloride. Examples are coconut agate and umbu agate. Snakeskin agate sometimes becomes too deeply blue, so as to obscure the inclusions rather than to enhance them by contrast. You should investigate this for yourself according to the nature of the gemstone you are using.

C. Ammonium Dichromate Treatment

This is an alternative method of providing a green background to copper inclusions. The green is different from that of Process No. 38A; it is more like chartreuse.

Prepare approximately a saturated solution of ammonium dichromate at the rate of about one-half pound to a pint of warm water. Select slabs of developing copper inclusions and immerse them in this solution carefully, so as not to dislodge the displacent metal (the bits of wire). The inclusions will continue to grow somewhat (this is variable), so allow for this in selecting the slabs. Allow the slabs with the bits of wire still attached to soak in this solution for at least three weeks. Pour off the solution, and store for re-use. Scrape off the wire bits, clean up the slabs, and they are ready for use.

This method works best for those agate varieties such as snakeskin that have taken on the deepest color as a result of the copper chloride soak. The others will be similarly modified but paler.

  1. If you should drop one of the bits of wire in the glass of copper chloride solution,pour off the solution at once and remove the bit. Otherwise it will continue to react with the copper chloride and decompose it.
Read also:

Gemstone Coloration and Dyeing – Table of Contents

By George W. Fischer
Copyright © George W. Fischer 1990
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