Slowly we are getting the main motives of the current Byzantine group work done. Next step is working on the background, which – very byzantine – is completely made of gold smalti. The gold stands for the divine light, the invisible, the Holy Spirit, infinity. As it reflects light, it makes the figures surrounding it light and lively.
In the ‘hell’ mosaic of the Baptistery of San Giovanni it is the gold glass that makes it so dynamic and contrasty. And that was certainly planned by its ideators, because the representation of devil and hell should make the believers in the Middle Ages anxious and devote. Thus, it had to attract a lot of attention and be legible from distance.
About 22 kilograms of gold glass will be used by us in the mosaic, with a mixture of Lemon, Gaggia and Oro Naturale (to enrich the mixture some rests of other types were added). With 200 € per kilogram that adds up with a substantial cost. Thus, before starting with the cutting, it was time for a short gold briefing this week. And this is what we have learned:
All gold? Different types of gold mosaic and their preparation
Gold stands for elegance and splendor, it enriches surfaces due to its beautiful way of reflecting light. Even in your mosaic projects, the material may accentuate and broaden your mixture. But how is the shiny glass manufactured?
Between two layers of glass, a sheet of gold leaf is incorporated: On a glass support layer (3 – 10 mm thick, transparent, opaque or red coloured) the gold leaf is fixed with a very thin protective glass layer (about 0.1 to 0.5 mm, called cartellina). With good processing the gold remains firmly attached between the substrate and the protective layer as the gold fuses together with the glass. From the glass plates with diameter of usually 10 cm, the 8 x 8 cm pieces or smaller smalti (1 x 1 cm, 2 x 2 cm) are cut with an oil glass cutter.
Types – Antique and modern
The oro antico, antique gold mosaic, is used for restoration purposes, because it has a used look and the gold is very close to the type that was used in Byzantine times. The gold leaf is particularly well merged with the support glass and is therefore broken. The usual hight of this type of gold is 5 – 6 mm. The glass support layer is – depending on the gold – colored yellowish to brown.
The oro moderno, the modern gold mosaic, has a very homogeneous gold surface and a height of 3 – 4 mm. The support glass is usually colored turquoise. The thin layer covering the gold leaf varies depending on the color of the final product from turquoise to red.
Colors – From copper to lemon
While antique golds can be found in few shades (usually white, lemon, yellow, orange and copper), there is a wide range of modern gold smalts: acid green, bright orange, burgundy, purple … the color palette is huge.
Surfaces – Flat and corrugated
Who wants to bring more movement into his mosaic, can use the oro ondulato (corrugated gold). It is prepared like the gold mosaic with a smooth surface, only that the supporting glass layer is pressed into forms that provide the corrugated top.
All that glitters ain’t gold – How to distinguish real from fake gold
And now the important question: How can I be sure that I am dealing with real gold smalts from Italy?
If you look at the gold tesserae, you see the structure described above: colored support glass, gold leaf, paper-thin glass layer. These layers are absolutely firmly fused together by melting – so the gold can not be destroyed by scratching. If you’re not sure, then cut a piece of glass and look at what’s happening with the gold leaf. Does it dissolve from the glass? Very bad sign. Is the piece of glass larger than 8 x 8 cm? Better stay away from it, as the maximum size of real gold leaf is 8 x 8 cm.
There are fakes whose false gold leaf is sealed with a thin plastic film. On others, it is simply glued on the glass support and can be easily scraped off.
Challenges working with gold tesserae
Who of you ever worked with the shimmering smalts, may already have encountered one of these difficulties.
The surface of the gold smalts is super flat (at least, if it’s not the ondulato). To obtain a clean cut, you should work with the edge of the hammer, not the entire surface (while still holding it very straight). A determined, but sensitive cut is the recipe for obtaining pieces without nasty quirks.
Another disadvantage of the smooth surface with almost no irregularities, is that it will prevent the piece from glueing well to the substrate. So always make sure that all smalts are firmly glued.
Low thickness of oro moderno
Apart from the gold smalti that have been produced exclusively for the Basilica di San Marco in Venice (thickness of 10 mm) or the oro antico, you will work with tesserae no thicker than 3 – 4 mm. Quite unpleasant for mosaicisti who normally create mosaics with a surface of at least 1 cm thickness, because the height difference of gold and other tesserae must be compensated by using more cement glue. Thus, the mosaic will prone to damage. So again: be sure that everything is firmly glued.
It seems a bit strange, but is actually true: Since the gold smalts (tiles of 8 x 8 cm and smaller pieces) are cut by hand with an oil glass cutter, its surface often has a greasy film. This prevents the cement glue to connect well with the glass. Therefor, it is recommended to clean the gold glass with a degreaser before using it.
Effect of gold often underestimated
Gold looks classy, not least because it reflects light in a beautiful way. Making surfaces from only gold smalts may sound seductive. Be aware though that the viewer could be blinded by the reflected light! A well-balanced mixture of different shades of gold (cold and warm, smooth and corrugated surface) and different inclinations help making the mirror effect of a golden surface less intense.
Also on the surrounding colors and materials, the golden material effects a lot. Pieces of glass that seemed bright and strong in your hand, can seem dark and bland when placed near to gold smalts. Anyone working with gold should keep this in mind and use colors that are more vibrant and strong than usual.
I hope these facts will help you when ending up in a gold rush in the future.
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