Although alchemy is often associated with gold-making, another essential skill of the alchemist is to color or dye stones like quartz (rock crystal) to look like precious jewels and gemstones such as carnelian and emerald. A few recipes have trickled down through time.
Pliny the Elder (c. 23 - 79 AD) records the existence of a long and established literary tradition dealing with the counterfeiting of gems and precious stones:
"Nay, even more than this, there are books in existence, the authors of which I forbear to name, which give instructions how to stain crystal in such a way as to imitate smaragdus (emerald) and other transparent stones, how to make sardonyx of sarda (banded onyx), and other gems in a similar manner. Indeed, there is no other kind of fraud practiced by which larger profits are made."
These dyed rock recipes come from the Stockholm & Leyden Papyri c. 300 AD. Although Pliny perishes in the Vesuvius eruption over 200 years before the papyrus is compiled, methods therein are known long before. By 600 BCE similar techniques are used to color glass.
Importance is placed on the application of alum, vinegar, and other substances to corrode or prime the surfaces of different crystals and stones before dyeing them the desired color. Best use of the various mordants can be found with experience and experimentation.
The term mordant comes from the Latin mordere, "to bite". In the past, it was thought that a mordant helped the dye "bite" onto the fabric or substance so it holds fast during washing. The best rocks for taking dye include quartz, selenite and topaz.
Corroding of Stones Method 1
"A corrosive for any stone. Equal amounts of alum and natron are boiled in an equal amount of water. The small stones are then etched. Previously warm them slightly near the fire and dip them in the corrosive. Do this for a while once to three times while the corrosive boils; dip and leave again three times but no more, so that the small stones do not break."
Coloring a stone involves the introduction of colored dyes into porous or fractured gems to alter their color. These fractures are intentionally created by heating the gem to enable better absorption of the dye by an otherwise non-porous material.
Corroding of Stones Method 2
"Let urine and alum putrefy and remain together with the stones for 30 days. Then take the stones out and stick them in soft figs or dates. These stones should also be worked on the coals. Therefore, blow with the bellows until the figs or the dates burn and become charcoal.
"Then seize the stone, not with the hand but with the tongs, and put it directly into the dye bath while still warm, and let it cool there. Make as many stones as you wish of, however, not more than 2 drachmas (each in weight). The dye bath should, however, be like paste."
How to Tell if a Rock is Dyed
When a stone is dyed, the color will appear more vibrant in certain areas where the dye tends to gather easily, such as cracks and textured surfaces, compared to smoother areas. Since the dye cannot uniformly penetrate the entire stone, there may be instances where scratches or chips expose a different color underneath the surface.
Preservation of Crystal
"So that it neither splits nor breaks. Take and mix the whole of a goose's egg with talc. Make it of pasty thickness and smear the crystal with it. Then put it in linen, bind this around it and leave 3 days in the dew and the sunshine. Untie after the three days and work the stone."
Preparation of Carnelian (Cornelian)
"Dissolve alkanet in oil. After that, put in the blood of a pigeon, and fine Sinopian earth and a little vinegar in order that the blood does not coagulate. Place selenite in it, close the vessel and place it amidst the dew for ten days. If you wish to make the stone very brilliant, arrange it so as to wrap it in horse hair, tie this on, and put it in the dye bath."
Sinopian earth is a mineral clay sold through the Greek port of Sinope on the Black Sea. The clay does not come from Sinope but from an region farther south in today's Turkey. Because it's marketed from Sinope and sellers keep their secrets well, it's called Sinopian earth.
Selenite is a type of clear gypsum, below. Due to its softness as a stone, it's more porous, and vulnerable to abrasions or scratches. This property lets dyes sink through the surface of the stone, and adhere better overall.
The softness of selenite makes it an ideal material for shaping into cabochons, which are smooth, rounded gemstones without facets. Selenite's gentle nature allows practitioners and artisans to carve and polish it into beautiful stones to showcase its natural translucence.
The cabochon style gem-shaping technique has been practiced for centuries, with historical records indicating that faceting gems, a more intricate and precise cutting method as below, did not become popular until the late 13th century.
Purification of a smoky crystal.
"Put it in a willow basket, place the basket in the boiler of the bath and leave the crystal there seven days. Take it out when it is purified, and mix warm lime with vinegar. Stick the stone therein and let it be etched. Finally, color it as you wish."
Preparation of Emerald
"Take and put so-called topaz stone in liquid alum (sulfate salt) and leave it there 3 days. Then remove it from this and put it in a small copper vessel in which you have placed pure unadulterated verdigris along with sharp vinegar.
"Put the cover upon the vessel, close up the cover, and gently keep afire under the vessel with olive wood for 6 hours. The longer you maintain the fire, the better and deeper will the stone be – only, as I say, with a gentle fire.
Cool and lift the stone out. Its condition will show whether it has become emerald. That is to say, you will observe that a green film has formed upon it. Let it become slowly cooled, however; if not, it soon breaks.
"Put oil in a small box-tree (Buxus, an evergreen shrub) vessel many days beforehand so the oil is purified and the product from it can be taken off. Put in the stone and leave it under cover 7 days. On taking out you will have an emerald which resembles the natural ones."
The term "emerald" is first used in the 14th century. Before that it's called smaragdus, meaning "green gem" in Latin, now synonymous with emerald. Emeralds, sapphires, rubies and diamond are types of beryl. Lab-grown emeralds are on the market since 1964.
Preparation of Amethyst
"Corrode the stones beforehand with three times as much alum as stone. Cook them in it until it boils thrice, and let them cool down. Take and soften krimnos with vinegar. Then take and boil the stones in it as long as you like."
Krimnos refers to the parasitic kermes insect which feeds on sap of Mediterranean and other oaks. A scale insect, it's used in dyes and concoctions and is one of the richest sources of red from nature. When processed it produces crimson, red leaning to purple.
During the Roman empire amethyst is an expensive stone, valued for its mythical properties of preventing inebriation in the wearer. It's a stone of Bacchus (Dionysus), god of wine. In the 18th century amethyst is discovered in Brazil. It's more common and less expensive today.
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