Question and Answer Page (3)
Questions and answers about miscellaneous glass related subjects.
Q. What are glass molds made out of?
A. First let me define molds. I consider a mold to be something that glass is either poured or pressed into, or simply melted inside of (as in pate-de-verre). It is filled with molten glass and the glass takes the shape of the mold. You get the same shape every time. Most of the time, this is the finished shape of the piece. There are other tools used to shape glass that are sometimes incorrectly referred to as molds. An example of these would be my paperweight shaping blocks. While these may look like a mold, they really are a shaping tool. The difference lies in the fact that one can use the paperweight block to obtain a variety of shapes, depending on the way the block is held and moved. A mold makes one shape, period.
There is a mold/tool that falls somewhere in between these two. This is an optic mold. Optic molds leave a pattern of some type on the surface of the glass. The glass is then manipulated further to achieve the final form and effect. A good example of one particular type of optic mold is a bubble mold. A gather of glass is blown or pressed into a mold which has a pattern of small diamonds cut into the inside surface. When removed, the glass has a series of small indentations impressed into its surface. More glass is gathered over this, and the indentations trap a series of air bubbles, which naturally round into small spheres as the glass is worked. If you have ever seen glass with evenly spaced rings of small air bubbles, and wondered how this was done - now you know.
There are lots of materials glass molds/tools are made of, depending both on how they are used and the cost factor. They range from wood (my paperweight shaping blocks are cherry wood) to steel and cast iron. Graphite is a good mold/tool material because it can handle heat, doesn't stick to hot glass, and is soft enough to carve easily. Wooden molds/tools are kept wet all the time or they burn up. Steel and cast iron are usually coated with a special oil to keep the glass from sticking to the hot mold. Graphite is used as is.
Q. Do you make your own molds/tools?
A. Yes, I make some of my shaping tools and buy some others. I buy my wooden shaping blocks from someone in West Virginia, and then modify them to suit my personal preferences.
As for molds - while I have used glass molds when working for others in the past, now the only molds I use are optic molds, and these I use just occasionally.
Q. How do you get glass out of a mold, especially something as thin as a light bulb or with a narrow opening at one end?
A. Molds are made in as many pieces as required to make the shape. There can't be any undercuts or the glass won't come out. Machine-made lightbulbs are made in a two piece mold.
Q. Can glass be drilled into and if so at what stage?
A. Yes, it can be drilled when cold, using a diamond tipped drill. Or, it can be drilled using a special steel drill and an abrasive grit (usually silicon carbide). One can also make reasonably accurate holes by pushing a sharpened, hot tungsten rod through the hot (but not too soft) glass.
Q. Does glass acquire texture only through molding or what?
A. There are a bazillion different ways to texture glass, molding is just one of them.
Q. I have always wondered how paperweights are created. Do you know of any good books that describe the technique.
A. There are many different techniques used, depending on the design of the paperweight. Floral lampwork weights are made by essentially sandwiching premade glass flowers (the pickup) between two gobs of clear glass. A gob of clear glass is heated to the point where it is very soft, then dropped onto the flowers. The glass must be soft enough to flow around the flowers without leaving air pockets (which will trap bubbles later). The second gob is then heated and dropped from the other side to completely encase the pickup. The weight is then heated again and shaped, using either wooden or graphite shaping blocks. (This, as you have probably guessed, is a very simplified explanation.)
For my Aurora paperweights, I pick up crushed colored glass with a gather of molten clear glass, heat it until everything is soft, and swirl the colors around. Then I make another gather of clear glass over everything, and shape it with wet newspaper and a wooden shaping block. A final firepolish to leave a perfectly smooth surface, and the weight is ready to be broken off the punty rod and placed in the annealing oven, where it will stay to cool slowly over the next 16 hours or so. (See "annealing oven" on Q and A Page 2.)
In the mean time, there aren't a lot of books with good info about making weights, but two tapes I know of that contain pretty good descriptions and photos of paperweight making techniques are: All About Paperweights (pgs. 41 - 45) and The Art of the PAPERWEIGHT (pgs.11 - 49) both by Lawrence Selman. There are some decent videos available, too. One of the two best I know is from Lundberg Studios, (although at this moment I can't lay my hands on any specific info about it). The other is "Nature in Glass", about Paul Stankard and his work. Both videos show detail of paperweights being made, Lundberg's from the furnace with torchworked details and Stankard's lampworked weights. The Stankard video is primarily a promotional tape from Larry Selman, but there are some good lampworking shots.
If you are ever in Corning, NY, check out the Rakow Library at the Corning Museum of Glass. They have an extensive collection of videos as well as printed material, and the best library staff on the planet. If you know what you want and when you will be there, you can call ahead and the materials will be waiting for you when you arrive.
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