Grading Glass and Graded Seals

In addition, Vycor can be shaped and/or formed while in its borosilicate state before it is transformed into Vycor. Thus, molded, pressed, tapered, and other shapes that would otherwise be very difficult, expensive, and/or impossible in fused silica can be done (relatively) easily with the pre-Vycor material with much less energy. Once the manufacturing is complete, the glass can then be processed to Vycor. 

Because Vycor already carries about 4% impurities, it is safe to dope Vycor to obtain characteristics such as color or UV opacity. Any similar doping of fused silica would alter the characteristics that pure silica strives to achieve. 

Finally, Vycor devitrifies far less than fused silica. Therefore, if you do not require ultrapure baking environments (similar to those demanded in the silicon industry), furnace tubes made from Vycor may be cheaper in the long run than those made from less expensive fused silica. 

Graded seals can be used to join not only different borosilicate glasses, but different types of glasses (and even metals) of different thermal coefficients of expansion. Obviously, it is most efficient and desirable to select glasses and metals with close thermal coefficients of expansion, because it reduces the amount of stress with which the glassblower must deal. 

Metals can be sealed directly onto glasses even though they may have radically different thermal coefficients of expansion. For example, copper or stainless steel can be sealed directly to standard laboratory borosilicate glass. However, to do this sealing, the metal must be machined so thin that any expansion is so (relatively) small that it doesn t overwhelm the glass. Unfortunately, by making the 

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