This article is an excerpt from the book “Gemstone Coloration and Dyeing“, written by George W. Fischer, and discusses tin inclusions from the section ” Chemically Induced Inclusions”.
Tin inclusions can be induced in agate and other gemstone varieties in much the same way as with copper. Just as copper inclusions are made from copper chloride, so tin inclusions are made from tin chloride. Copper chloride imparts green and finally blue-green color to the agates, but tin chloride is colorless unless it happens to have some native color of its own. Furthermore, agate with induced tin inclusions does not lend itself to complementary color variations like the copper included agate does. It seems that, with few exceptions, slabs that have been impregnated with tin chloride will not absorb additional chemicals in solution.
Tin Inclusions – The Basic Process
- Tin chloride (stannous chloride), SnCl2
- Ferrous sulfate (alias copperas, green vitriol, iron sulfate), FeSO47h20
- Hydrochloric acid (muriatic acid), HC1
- Aluminum metal (aluminum wire, preferably 10-12 gauge)
- Washing soda (sodium carbonate), NaCO3
- Rubber bands (size 16 preferable)
- Tooth picks
- Prepare approximately a saturated solution of the tin chloride. This will require about two pounds of the tin chloride salt to one pint of water (room temperature, not warm). Add the tin chloride to the water while stirring and stir until it is entirely dissolved or no more will dissolve. To this solution add hydrochloric acid at the rate of about one-fourth cup to a pint of solution. Immerse clean, dried slabs of suitable agate or other gemstone in this solution one at a time, and leave them there for at least two weeks. Pour off the solution, and store for re-use. Rinse the slabs lightly and wipe dry with paper toweling.
- Straighten out a piece of the aluminum wire (any convenient length) and draw it through folded sandpaper until it is clean and shiny and the raw metal is exposed. Then with snippers or wire cutters, cut the piece of aluminum wire up into pieces approximately one-eighth inch long. Lay before you on the table where your are working, the slabs, the pieces of wire, the rubber bands, a small glass of the tin chloride solution and a pair of tweezers or small, sharp pointed forceps.Criss-cross a rubber band over a slabs of the tin chloride soaked agate. Lift up a portion of the rubber band, dip a toothpick in the tin chloride solution and place a droplet on the slab under the rubber band and where you wish a tin inclusion to develop. With the tweezers or forceps, pick up a piece of the aluminum wire, place it in the droplet of solution, and carefully let the rubber band down on the piece of wire so as to hold it there. Do this in several places on the slabs, according to the size of the slabs, allowing adequate space in which the inclusions can grow. Do the same with all the slabs you have ready to “inoculate”. Leave these inoculated slabs on the table several hours or overnight.
- Prepare a saturated solution of the washing soda, as for procedure C of Process No. 36, or use the same solution if you have it on hand. Immerse the tin inoculated slabs in the soda solution as prescribed for copper inoculated slabs in Process No.36. The tin inclusions tend to grow more quickly than the copper, so they will bear closer watching. When any particular colony of inclusions has reached the desired stage of development, terminate the growth simply by dislodging the piece of aluminum above it. Leave it in the washing soda solution however. Allow all inoculated slabs to remain in the solution for about four weeks. Pour of f the solution, and store for re use. Remove the rubber bands and the pieces of aluminum wire, clean up the slabs, and they are ready for use.It is almost imperative that the pieces of aluminum wire be fastened down, as with rubber bands. Otherwise, they are too easily dislodged, even merely by immersing the inoculated slabs in the soda solution. Aluminum is a very light metal.Besides aluminum, zinc is a good, active metal to displace tin and form inclusions. However, it seems to work too fast and to produce colonies of inclusions that are too dense. Theoretically, there are several other metals that should displace tin. Of these, I have tried iron, cadmium and magnesium, but with negative result.The tin inclusions produced by this process are not only moss and plume; sometimes radiating fans or platelets of tin are formed, I have had best results with snakeskin agate in this process
Tin Inclusions – Complementary Coloration
Since the process for inducing tin inclusions lends absolutely no color to the included gemstone, it follows that complementary coloration is sometimes desirable. This is not as readily accomplished as with copper included agate, however. I have tried many theoretical possibilities and all but two resulted in ugly discoloration or none. One of these two usually lends a nice rose quartz pink to the included agate (snakeskin) and is accomplished with cobalt chloride. The other is pale green with chromium sulfate as the coloring agent.
A. Cobalt Chloride Treatment
This process is an adaptation of Process No. 12 to tin included agate. The procedure is simple. To a saturated solution of tin chloride (Process No. 39) add as much cobalt chloride crystals as will dissolve therein. The resultant mixture will be much like a normal solution of cobalt chloride (as for Process No. 12).
The rest of the procedure is the same as for Process No. 39. Allow the soaked slabs to soak for the same length of time, inoculate the slabs in the same way and incubate them in soda solution the same way.
The presence of cobalt chloride with the tin chloride in the same slab does not seem to interfere with the displacement of the tin to form inclusions, but it does impart nice pink to the slabs, reminiscent of rose quartz. The result is silvery inclusions in a pink background and is very attractive.
B. Chromium Sulfate Treatment
Dissolve as much chromium sulfate into any desired quantity of tin chloride solution as the solution will take. After soaking slabs (snakeskin recommended) in this mixture, inoculate and incubate them in the same manner as prescribed above for Process No. 39. This treatment results in a light grayish-green background for the tin inclusions.