Aurifiction - imitating gold
The eleventh chapter of the Rasaprakāśasudhākara contains 20 recipes for making gold, improving the quality of gold, or imitating gold. The recipe of our current experiment is for making copper the colour of gold. Aurifiction, not aurifaction.
The formula is deceptively simple.
ताम्रे सप्तगुणं नागं वाहितं पुनरेव हि /
तेन ताम्रेण रसकं सप्तवारं च वाहयेत् // ५४ //
स्वर्णवरणं हि तत्ताम्रं जायते नात्र संशयः // ५५ //
Seven parts lead are amalgamated with one part copper.
Then, likewise, one should amalgamate seven parts zinc with one part of this copper.
The copper will take on a golden colour without doubt. (RPS 11.54-55)
Three metals are amalgamated and hey presto! Imitation gold.
Well, it turned out to be not quite so simple.
We began by deciding that seven times the amount of lead to one of copper refers to size rather than weight. Andrew prepared ingots of the same size accordingly.
[Seven pieces each of lead and zinc to one of copper]
However, our initial discussion also concerned whether or not the lead, zinc, and copper should be purified prior to their amalgamation. The recipe does not specify that they should be purified (śuddha), but Andrew argued that purification of substances is always implied in rasaśāstra contexts. This is generally true. The processing of materials before they are applied in the formulation of an elixir or medicine is the hallmark of the Indian alchemical and iatrochemical tradition. These procedures are not purification in the sense of gaining pure elemental copper (Cu), or lead (Pb) or zinc (Zn), as other substances may be added to them in the process. Purification procedures are understood to remove harmful contaminants or unwanted characteristics from substances, to potentiate them, or to extract their essence. Which procedures are applied depends on how the substance is categorized. The Rasaprakāśasudhākara describes procedures for purifying copper, lead, and zinc in its fourth and fifth chapters.
However, this may be unnecessary. The eleventh chapter of the Rasaprakāśasudhākara stands apart from all other chapters of the work in that none of its recipes refer to a medical application of their products. What exactly they are meant to be used for is unclear, though a few recipes mention that a product will be “suitable for the market”. I assume their intended use is for jewelry, or for lucky charms, not for any internal use. Therefore, the purification procedures may not be required. However, this really goes against the grain for anyone trained in the pharmacological discipline of rasaśāstra and so we agreed that we would prepare two batches: one with purified copper, lead, and zinc, and one with unpurified components.
We started with the unpurified components. Andrew melted the copper, as it needs the highest temperature at ca 1100 °C. He then added the lead, and, once this had melted in the copper, he cast the amalgam into an ingot mould. The mould is made from cuttlefish bone, which is a material that is soft enough to be carved like soapstone, but can also withstand astonishingly high temperatures.
[copper-lead amalgam being cast into the cuttlefish mould]
He then reheated the amalgam until it was liquid again. It is not totally clear from the recipe whether one is supposed to cast the amalgam in between, or whether the zinc could have been added right away.
Adding the zinc is a dramatic moment: as it oxidizes, it sizzles and produces smoke - you wouldn’t want to stand too close. Andrew stirred the liquid metals and then poured the amalgam into the mould.
Here’s the result.
[amalgam of copper: 1 lead: 7 zinc: 7]
Well, not exactly what we had hoped for. It would look a bit better if we polished it, but it would still be mostly silvery. And the alloy was uneven – the metals did not properly amalgamate. Failure!
We reconvened to discuss our options. Andrew suggested flipping amounts: 7 copper to 1 lead and 1 zinc, to make sure the colour would be more on the yellow side. This was rather a departure from the recipe. I looked for a parallel recipe in the other alchemical works to see whether they suggested different ratios. However, I could not find an exact correspondence. The closest recipe was one from the Rasārṇava (chapter 12, verse 51):
तीक्ष्णं नागं तथा शुल्वं रसकेन तु रञ्जयेत् /
समस्तं जायते हेम कूष्माण्डकुसुमप्रभम् //
One should dye sharp iron, lead, and copper with zinc.
Combined, gold arises that gleams like the flower of the wax gourd.
Not exactly the same, as it adds “sharp iron” (tīkṣṇa – wrought iron or carbon steel?) to the recipe. Note also, that this recipe claims that gold is produced rather than that copper will have the appearance of gold. This recipe does not give ratios at all, which we felt gave us some justification for our change of ratios in our original recipe….
[new ratio - copper: 7 lead: 7 zinc: 7]
[copper in the crucible]
We may have been grasping at straws. Long story short: applying the different ratio also did not quite yield the result we were hoping for. Slightly better colour, as you can see here:
[amalgam of copper 7: lead: 1 zinc: 1]
But far from resembling gold.
Luckily, Andrew has a friend who is a bronze caster and was able to consult with him. The friend suggested two main fixes: First, melt and then amalgamate the metals with the highest melting points. This changed the sequence from copper – lead – zinc to copper – zinc – lead.
Second, use something to stop the metals from oxidizing. He initially suggested placing charcoal on top of the metals, and then reminded Andrew of an experiment in which Andrew had successfully used jequirity beans (guñjā) for this very purpose. Andrew had come across this usage in Bhagwan Dash’s Iatrochemistry of Ayurveda (2002, page 386). There, jequirity beans are mentioned as one of the “group of five friends” (mitrapañcaka): “Honey, ghee, guggulu, guñjā and borax are called mitrapañcaka (five friendly ingredients). These ingredients, when added to seven types of metals, etc., and blown over fire help in their combination.”
The mitrapañcaka are already mentioned in the Rasaratnākara (Vādakhaṇḍa 2.11), but the passage does not mention their use in aiding in amalgamation.
We decided to use them. And this turned out to be fairly key: the resulting amalgam turned out to be much smoother, and indeed, after some polishing, quite gold-like! Well, we essentially made brass. But still. We’ll count this as a success.
[jequirity beans - guñjā]
[jequrity beans in the crucible (copper, zinc, and lead beneath)]
[Gold! Well, gold-like amalgam. Sovereign for colour comparison]
Here is the film of this experiment. This time, the video contains our behind-the-scene discussions on how to go about the procedure.
At the beginning of the experiment, we had decided to do two batches: one with unpurified and one with purified materials, so now that we had worked out a good method, we made one more batch, this time first applying purification procedures to the copper, zinc, and lead. The Rasaprakāśasudhākara gives instructions for purifying lead and zinc in its fourth and fifth chapters. It also gives instructions for purifying copper. However, instructions for the latter are a bit vague, and we therefore decided to apply procedures that Andrew was familiar with from his training, and that incidentally fit with the instructions for purifying zinc.
Chapter 5, verse 123 reads:
Melted and quenched in sour gruel, or else in buttermilk, or human urine, or sheep urine, zinc will become properly purified.
Instructions for lead are found in chapter 4, verse 96:
One should break down lead in the juice of turmeric and chaste tree.
Thus lead becomes purified and does not cause fainting, swelling, etc.
For zinc (and copper), we decided to go with buttermilk. You can see the purification procedures in this film:
The first film shows the outcome of using purified materials at the end. The result seems a bit better in colour than the other batch.
[purified and unpurified]
However, this may simply be an outcome of Andrew having gotten the hang of the procedure. Really, the recipe calls for metallurgical knowledge more than chemical knowledge. It’s difficult to understand the ratios given in the original recipe. Even using jequirity beans to hinder oxidation, the resulting ingots would have too much of a silver colour. Here, the question remains whether this is simply a wrong reading, perhaps due to a faulty transmission (we do not have a critical edition of the Rasaprakāśasudhākara), or whether the author was deliberately misleading the readers. I doubt the latter, because, after all, the recipes for coral and pearls worked out (more or less). Work on the other recipes for gold imitation or making may show similar results. And an examination of the extant manuscripts may throw further light on this question.
[Map of manuscripts of the Rasaprakāśasudhākara in archives in India. Map created by Keith Cantu]
We decided to make one last batch, this time using the ingredients listed in Rasārṇava 12.51, and applying the ratio we had been using for our most recent batches. And this yielded the probably best results.
[copper-iron amalgam, copper, zinc, and lead]
[results before filing]
[results after filing]
See the film of this last experiment here: