"Glass batch calculation or glass batching is used to determine the correct mix of raw materials (batch) for a glass melt.
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The raw materials mixture for glass melting is termed "batch". The batch must be measured properly to achieve a given, desired glass formulation. This batch calculation is based on the common linear regression equation:"
http://en.wikipedia.org/wiki/Glass_batch_calculation

"Adjonction et dosage des composants: Verre recyclé, feldspath, carbonate de sodium,
oxyde de fer, oxyde de manganèse, sulfate de sodium, nitrate de sodium
2 Dans le four de fusion règne une température constante de 1250° C
3 Le verre fondu sort du four"
http://www.foamglas.ch/__/frontend/handler/document.php?id=5...

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Note added at 19 mins (2013-08-27 07:10:15 GMT)
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Question précédente, "patterns" : pourrait-il s'agir de vitraux?

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Note added at 2 hrs (2013-08-27 09:48:28 GMT)
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"From many years ago the glassmaker was adding substances to glass's raw material or batch to produce coloured glass.
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This type of knowledge is used in decolourising glass, which must inevitably contain a small percentage of iron impurity. Iron oxide (FeO) in the form of ferrous iron will give a bluish-green tint to the glass, whereas in its higher state of oxidation as ferric iron, it gives a yellowish-green tint, which can be masked by the addition of complimentary colours such as red and blue. To ensure that most of any iron impurity is in its ferric state, oxidising agents such as sodium nitrate (NaNO3) are added to the batch in small amounts. The oxidation of iron is known as chemical decolourising whilst by masking the green with red or blue is called physical decolourising and is achieved by the addition of cobalt and selenium oxide.
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There are also other factors, which have to be taken into consideration when producing Coloured Glass: -

1. The temperature of the melt/batch Old print of glassmakers at work in a glasshouse
2. Temperature of reheat during the working of the glass
3. The temperature of the 'Lehr' (Annealing Oven)
4. Duration of the melt/batch "
http://1st-glass.1st-things.com/articles/glasscolouring.html