Glass moulding

Mould preparation

The original model, generally in baked clay can also be made out of another material. A negative print in elastometre is taken from this clay - mixture.
From this first mould, a wax is made.On this wax a « maselotte » is carved, it is a funnel-shaped device made of wax too.The whole is cooled with heat resistant product (plaster and chamolte to water) the fabrication of which is very important. To be able to bear the retraction of the moltenglass, during the rising of temperature, it does not need to be befecther stiff or less its cohesion at the melting-moment (at 900°) Processing a sculpture in glass with lost wax, reveals most of the time, the melting of art bronze used to remake (artistic works of sculptor)
When wax is removed from the mould, then glass can be moulded for use.

(The mould emptied from wax is ready to receive the glass)

Preparation of the tint

When the piece is to be tinted, a combination of colours is prepared by mixing oxides and crushed glass in a pot, the whole is heated at 900° for nearly 10 hours for a final homogeneous colours, this preparation is ground and mixed to glass as it getting meted to tint it in mass .The effects of colour setting depend on the thickness of the grains glass blocks to be tinted and the way the latter get mixed to the colour powder.
If the colour is not the same all over, the mould will be done many parts in order to get it open.
For an external colour, a mixture of tint powder and sodium silicate is spread inside the mould by means of a brush.
A big part of resarch and molten glass concerns the colouration it consists in finding out the best oxide, (scarce earth) proseodynum and lead carbon, and purple from manganese.
The artist can elso get ready made tints, but they do not have the same glistening. Up to now, it is difficult to achieve the red tint from a mixture of different oxides.

Baking

A part of this method is empiric and is similar to some trustworthy proceedings. For example, some average not very famous, nothing better has found than a sympathic and so plain flower pot in red clay with a drainage hole, to receive the mixture of glass and colour in more or less cruded glass pieces and colours. It is set on a filter in biscuit aiming at minimising the bubles.
Once the oven is closed the melting increases gradually heat them the temperature decreases in succeeding steps.
It will need a low cooling process in the oven, which can take many days long according to the importance of the work followed with an extra-baking aiming at discarding the internal tensions.

Polishing and finishing off

When the whole piece is cooled, the mould is drawn, the masselotte* cut up with a dimond-tipped saw.
Small piece of metal-used as an extra part added to another one and the work is dished by buffwheel and glasspoper to take the flaws from the surface, the microbulbes...
Once it becomes smoother and neater very thin it is sanded homogeneously by means of a sand casting process .
In case of crystal, polishing is different, the masselotte is drenched for time into fluorhydric acid an operation which without lead, would on the contrary tarnish the glass.

 

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