Making Our Glass

The Furnace

Crucible or Pot normally found inside a glass furnace

The furnace runs constantly, and is only ever turned off for general maintenance every few years or in an emergency. Inside the furnace is a large crucible or pot which holds up to 100kg of molten glass. It is refilled (or 'charged') every few days as required. If large items are being produced it will need to be charged more often than when smaller pieces are being made. The charging process generally takes place in the evenings, when small amounts of Batch are shovelled into the furnace and then allowed to melt down before more is added.

 

Clear Or Blue Glass?

Once the Batch is melted down, the natural glass is colourless. We work with this colourless glass to create  our range of clear and brightly coloured items. By adding Frit and Colour Bar to the clear glass the glassblower can use simple techniques to create unique designs of dots, lines and swirls within the glass.

Taking Glass out of the pot so that the colour can be changed

However, every one-three weeks we add small quantities of copper oxide & iron oxide directly to the pot to turn the glass blue.  During this time all the items we produce will be Aqua in colour.  We can add other colours with Frit or Colour Bar but the piece will always be tinted with our signature aqua blue.

To return to clear we must empty the pot of all the blue glass before refilling with clear, this can be saved and remelted later.  If any blue is left in the pot the next few items made will have a very pale hint of blue.  This is quite rare however, so if you find a piece with this colouring it is considered extra special!

This rotation of pot colour means that if you place an order with us for an amber vase whilst we are working with the Aqua glass your order may take much longer than it would if we were working with clear.

Annealing

Once the glassblower has finished hand crafting the glass, it is placed in the lehr (or kiln).  The glass remains in this digitally controlled lehr overnight so that the glass can cool down slowly and in a controlled manner.  If the glass was simply left to cool outside, it would very quickly crack due to thermal differences within in the glass.

Recognising Free-Blown Glass

Free-blown glass is identifiable from mould-blown glass by small characteristic marks left by the glassblower.

A Punty mark will often be present on free-blown glass, this shows where the glassblower removed the piece from the blowing iron and attached it onto another support or Punty (Bridge of Glass) to work on the glass from another angle.

Slight tool marks may be evident where the glassblower has used metal tools to push and shape the glass.

Slight differences in size and design prove that pieces have been hand crafted.  Mould-blown glass can be replicated thousands of times, with each piece being identical to the one before.  Free-blown glass will always have an element of humanity within it as each glassblower leaves his own mark on the piece.

Glass Making Terms

Batch - The raw materials of glass before being melted together in the Furnace.  Made up of 65% Quartz (sand - the 2nd most abundant mineral in the Earth's Continental crust) and a mix of Potassium Carbonate, Sodium Carbonate and a few other ingredients.

Frit - Small chips of coloured glass that can create dots or swirls of colour when melted into a piece.

Colour Bar - A dense piece of coloured glass that is melted slightly then applied directly to the work in progress, this is a lengthy process so can be a beautiful but costly design feature.

01225 428146 | sales@bathaquaglass.com
 

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