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about granulation
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This is a technique used in ancient gold work
and involved soldering little golden spheres, known as grains, onto a background, generally foil, following a predetermined pattern.
When the grains reach microscopic proportion – ones as small as 0,1 mm in diameter have been measured – the same technique is given the name of “dust”.
This is a one of the most complex and fascinating techniques in the jeweller’s craft and is one of the most disputed at the same time.
This is because opinions regarding the application methods are disparate and conflicting and the various hypotheses formulated today have not yet provided reliable concrete results in experimental conditions.
To proceed in order, there are essentially two problems regarding the working methods used by artists in the past which have been debated at length by scholars:
A) The system which allowed the production of considerable quantities of grains which have been found to have a constant calibre in some works.
B) The technique used to solder the grains to the supports for the points of contacts are barely perceptible even when highly enlarged under the microscope.
Some of the main hypotheses formulated over the years include:
A – for the production of the grains
- Molten gold poured through a sieve with the drops falling into a basin of cold water.
- Melting of a fine gold thread, letting the molten metal drop into a container full of charcoal dust.
- Uniform cutting of tiny fragments of gold thread or leaf, mixed with charcoal dust and taken to melting point.
- Filing of gold, mixing with charcoal dust, and heating to melting point.
- Melting of fine gold thread and letting the drops fall onto a sheet of iron or marble, or between two metal sheets.
B – for the soldering technique
- Soldering by means of a gold/silver/copper soldering alloy with a lower melting point
- Formation of a surface layer of gold carbide on the little spheres by leaving them at length in charcoal dust.
- Addition of small quantities of tin, whatever the soldering alloy.
- Self-welding with heat only and without the addition of any external material
- Use of copper salt and organic adhesive.
Numerous publications have been dedicated to the topic in specialist reviews and in academic environments.
Nevertheless many problems relating to the ancient technique of granulation still remain unresolved, and the technical processes associated with them have not been clarified.
Recent investigation shows that it is highly likely that different processes and materials were used alternately.
These differences can be attributed principally to three variables which can be found in any historical period:
1) The artist’s skill
2) The place of production
3) The customer’s tastes
For the jewellery of the Orientalizing period, which includes some of the most beautiful objects ever crafted by man from gold, and in which the techniques used, including granulation, reach the maximum applicative heights, the most plausible methodologies are the follows:
A - for the production of the grains
Tiny fragments of gold are mixed with charcoal dust; the starting materials can be differentiated on the basis of the quantity and diameter of the grains to produce.
Then, when these fragments are heated to melting point they melt and form gold spheres which can subsequently be separated from the charcoal dust and cleaned.
After cleaning, the grains which are not perfectly spherical are eliminated while the remaining grains are sorted according to their size.
This latter procedure can be carried out using sieves with meshes of different sizes.
B - for the soldering technique
Colloidal soldering or soldering with a copper salts. This method envisages that the copper salts, mixed with animal charcoal or vegetable glue, are positioned at the soldering points in such a way that the glue “carbonizes” during heating to create a reducing environment; by reducing themselves to metallic copper in this way the salts fuse into an alloy with the gold and lower its melting points.
As a result, the grains, the leaves, the threads and all the decorations join together and to the foil at the points of contact only, in a stable and imperceptible manner.
This hypothesis seems to be supported by analyses carried out on several finds in which the presence of copper in the gold alloy, in the areas of contact, is much higher compared with others, while the silver content remains proportionally constant.
Nevertheless, the passages required for realizing the soldering procedure seem excessively complex to be able to ensure output at a high quality level.
In other words, the method just illustrated could certainly work, but only the make objects with much sparer decoration (filigree and granulation) than that on the jewels which have come down to us, such as in the case of the Praeneste Chalice (Victoria and Albert Museum) which has hundreds of thousands of tiny spheres.
Something that is worth remembering, but does not seem to be noticed, is that there can be no doubt that in the ancient world, and for reasons which should be even more obvious, all the tricks relating to production economics aimed at saving time and materials, and simplifying – and therefore speeding up production – were applied.
This does not mean that the cost-cutting, high profits or fast output took priority over or were in contrast with the quality of the work, but that all these needs had to be taken into consideration by the craftsman-artist who, precisely for this reason, became smart and devised new techniques.
To do justice to the huge amount of work required to produce the masterpieces which have come down to us from antiquity, each finely conceived and worked, we must therefore image a simpler, more immediate procedure, one which is not necessarily less ingenious.
The works of Akelo – Andrea Cagnetti that such a procedure was not only imagined but was also put into practice.
© 2002 Andrea Cagnetti/Paolo D'ambrosio - Tutti i diritti riservati
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