How to evaluate the quality of glass
Visual Concerns Top
Bubbles are nearly impossible to avoid. Obviously there are numerous variants to this rule, but assuming a proficient and conscientious gaffer the bubbles you may see are generally caused by the manufacturer of the color not the glass artist. Here's how it works. One of the manufacturers of glass color creates a huge crucible of a certain color. The appearance of this transparent color is always dark black and it is opaque to light. Their color gaffers create a color bar by gathering layer upon layer of the black substance and rolling it on the marver in-between gathers. Invariably, small bubbles are created in-between the layers. These are the bubbles you often see in the finished product. It is impossible to see these bubbles until the color is stretched thin enough to let light through; unfortunately this is the point that the piece is nearly finished. So, we live with these small bubbles.
There are other bubbles that are the artist's responsibility. These are usually located outside the color layer in the clear layer of the piece. Generally these come from gathering over the previous gather and picking up a bubble from the crucible. These should not exist, but realistically the small ones will probably be allowed to remain. It is important to note here that a very small bubble, say the size of the head of the proverbial pin, can result in a bubble up to 1⁄2" in diameter once stretched out fully. So for the most part we're dealing with minute problems that can compound into real flaws.
Lip and Edge Control Top
The lip of the piece is another easy indicator of the skill the artist has mastered. When "necking" a piece to prepare for the punty the artist will use "jacks" to constrict and to chill what will ultimately be the lip of the piece. This contact with the special steel leaves a mark logically called a jack mark. This mark should not exist. The glass should be clear and smooth. Another poor quality technique is to cover the jack marks with a "lip wrap". It's kind of like hiding a 1⁄2" gap in the flooring with carpet, you'll probably get away with it, probably.
Chill marks on the lip should not exist. They look like surface cracks with smooth edges.
Punty Issues Top
The punty is the device that allows the artist to change ends. It is quite acceptable to leave the "punty mark" on the bottom of the piece as long as it is not exposed. The punty mark is one of the signs of a blown glass object as opposed to a cast glass object. There should be no sharp edges and the piece should sit flat against the table without any rocking. Some artists polish the bottom of the piece, but this is mostly personal choice unless looking through the bottom of the glass can see it and hence causes a visual distraction.
Body of the Piece Top
- The body should be free of paper burns, chill marks and cords. Paper burns are small bits of ash that stuck to the glass when cooling and shaping. They look like dull spots in the layers. Chill marks are uneven waves of glass; they refract light differently than the surrounding area. And finally cords are waves of glass that look like strands of material that refract differently than the surrounding glass.
- Obviously there should no folds, cracks, holes, nicks, scratches, or any other visually distracting artifact. Note, some artists may purposefully use some of the above "problems"; use your discretion.
- Color. Generally the color should be consistent throughout the piece. Many exceptions to this rule exist however, so again use your discretion. As an aside, the deeper the color or the more color used greatly increases the difficulty of the piece. The technical issue is that different colors will absorb heat at different rates hence they will also dissipate heat at different rates. An even bigger problem exists when different colors, which react at different rates, are combined. For instance, enamel white is very stiff and when combined with some diffuse colors this white will act as if you were combining concrete with molasses . . . not a great fit. The same happens with heat, this same enamel white will deflect heat (keeping it cooler and hence more stiff) and when combined with a green that readily accepts heat compounds the disparity that existed due to the physical property of the color. It has taken years to learn how to combine the intense colors in Glass Act™ art and in fact this technique is the hallmark feature which visually separates this work from nearly every other artist.