Glass blowing has been a skilled craft for over two thousand years. The ingredients of sand, soda ash, lime and colorants are mixed together in a furnace crucible and heated to 2400° Fahrenheit, at which temperature the ingredients melt together and any bubbles within the batch escapes. After the temperature is reduced to 2000° Fahrenheit, a “gather” of glass is picked up using the pre-heated end of a blowing pipe. A bubble of air is formed within the glass gather using the force in a person’s lungs. By reheating the glass bubble as needed in the glory hole of the furnace, it can be further inflated to the size needed for the job in hand. Shaping is done using soaked wooden forms and paddles, and metal shears and one-piece molds. During the entire shaping process the glass must be kept in rotation to prevent it from sagging into itself and ruining the vessel. Once the glass piece is the right size and shape, it is transferred to a solid metal rod called a punt. As a part of this process, the glass is cut from the blow pipe and the opening can then be formed into the desired shape: a round even lip for a cup or a bowl, a flared dish, the pouring spout of a pitcher, or the gather can be shaped into a flat round circle. Additional glass embellishment can be made at this time, like an edge of a different color, or a handle added to a pitcher. When all work on the object is completed, the finished shape is cut from the punt into the arms of another glass worker wearing an asbestos apron and gloves, who places the object into the annealing oven where the rate of cooling can be controlled and thermal shock avoided. The glass blower then gets a new gather of glass and the whole process is repeated. To function smoothly, there are usually three or four helpers for each glass blower, and teams that have been together for a while perform the glass dance with few words and the grace of those who have mastered their craft. If you ever get a chance to watch this process, do so. It is fascinating.
Machine-molded glass vessels are made by pressing the correct amount of glass between two forms. The hot glass is extruded from the furnace in a long bar. The appropriate amount of glass is cut from the bar and falls into the heated outer mold. The heated inner mold presses down until the glass is formed into the desired shape. Once the inner mold has retracted, the molded glass form is lifted from the outer mold. Reheating the glass melts it just enough to round the edges and in some cases remove the mold marks. If this is not possible, the mold makes can be removed by grinding or polishing the glass object once it has been annealed.
Go to the Table of Contents to see all topics covered so far.
Click glass collectibles to go to the most recent entry on this site.