Method of Manufacture

There is a common misconception regarding glass and crystal and most people do not think about how a piece of glass has been made.  Machine making will usually not result in their being any bubbles in the glass, while mouth blowing almost always will – and this is a hallmark of mouth blown glass.  To us, this hallmark adds a sense of value.  Of course, there are acceptable levels of bubbles and our suppliers of mouth blown glass are well aware of the acceptable levels.

Machine Made - Pressed

The Stern and Haworth Tankards on our website are Pressed (there is a mould line opposite the handle).  This is the least expensive way of producing an item and it shows!  However, it is not possible to Blow a Tankard by Machine... only by Mouth.

Machine Made - Blowing

Bowls of wine glasses are mostly Blown by Machine. The stems of wine glasses are usually Pressed - then the glass is assembled using gas jets.  This is not the case with our Balmoral Glass, which are entirely made by hand/mouth.

 

 An inexpensive, machine made tankard.

"Stern" Tankard.  Inexpensive, machine made glass.  Able to be engraved for all occasions.

Hand Made - Mouth Blown

The mixture, named a “Batch” is put into pots in a Furnace.  Sometimes, 'cullet' is added. Cullet is waste glass or glass from a previous batch.  It acts as a catalyst to bring the sand and oxides up to temperature quickly.

The ‘softening point’ for Lead Crystal is approx. 600°C  and the ‘moving point’ is approx. 800° C.   For Soda Glass the moving point are higher (around 11000C, which is why we can Decal Transfer Print on Soda Glass, but not Lead Crystal.

Usually, a team of glassworkers (named a ‘Chair’ of Glass Makers) consist of a Servitor (Blower), a Foot-maker, a Bit-Gatherer and a Taker-In.

Any glass made into a shape by air pressure (whether by mouth or machine) is referred to as blown glass.


 

"Stern" Tankard.  Inexpensive, machine made glass.  Able to be engraved for all occasions.

Glassblower, blowing glass, on loan by © SFP.

The Bit-Gatherer gathers the molten glass from the furnace on his Blowing Iron. This is rolled into a ball (named a Gob of Glass) and lightly blown, before he passes the Blowing Iron to the Servitor, who continues to blow the bubble and Marvers it, using a shaped wooden tool. The final shape is determined by turning the Gob inside a wooden, cast iron or steel mould. Wooden (Cherry or Beech Wood) moulds require replacement more frequently because they ‘burn’, due to the molten glass.

Assuming we are making a Wine Glass; the bowl is formed and while it is still extremely hot, a small amount of molten glass is attached to the base, to make a Stem.  The Stem is ‘worked’, using a variety of tools and further wooden moulds, to shape it.  Another small quantity of molten glass is added to make the Foot and a different set of tools are used to shape that. The glass is ‘broken’ from the Blowing Iron using a drop of cold water and taken to the Annealing Oven by the Taker-In.  There is a continuous ‘stream’ of glass gathered, blown, shaped and placed in the Annealing Oven.

Annealing 

The glass is paced into the Annealing Oven (named a Lehr - an oven with a roller bed approx. 80 feet long, where the heat inside decreases steadily as the glass travels through) and comes out the other end about 3 hours later.   This process allows all the molecules of the glass time to align.  This gives the glass far greater strength in use.

Quality Control

The glass is inspected for flaws; large bubbles or ‘striation’ (most of the first 50 or so pieces being made will have striation - like a streaked cloud across a sky), due to the cold temperature of the moulds and the sheer heat of the molten glass. Rejects are used as cullet (re-used in glassmaking as a catalyst to make the sand and oxides melt faster).

 

An Annealing Oven.

Annealing Oven photograph, kindly loaned by ©

Hangzhou Hangshen energy-Saving Furnace Co., Ltd

Finishing

The rims of glasses have a rounded top after blowing (named a Moil). This is removed, using a diamond cutter and then slightly rounded in a fine gas flame. An alternative is to grind the tops by holding against a Carborundum wheel and then smoothed to a rounded finish.

 

- All about the History of Glass and where it all started.

 

- What Glass is made from.

 

- What is "Cut Crystal" and how is it achieved.

 

- The different ways glass & crystal can be personalised.

  - Sandblast engraving Glass & Crystal.
  - Information about hand engraved glass & crystal.
 

- The things to look for in Glass & Crystal

 

- How to look after your glass & crystal, plus cleaning tips.

 

If you have any questions, our knowledgeable staff are on hand to answer them.  Simply Contact Us.