Once one of the most popular forms of glass manufactured in the UK, lead glass is seeing somewhat of a renaissance in popularity in recent times. Though not suitable as panes for your windows, it’s a marvellous form of glass that can be utilised in very many interesting ways.
Containing the compound lead oxide (PbO), lead glass was discovered in the 17th century by George Ravenscroft sort of as a byproduct of them trying to repair their companies reputation. In those days glass manufacturing wasn’t as simple (or at least as automated) a procedure as it is nowadays. Impurities could easily find their way into the mixture, and as they tried to perfect the art of glass making, manufacturers would often include various alkaline salts and quantities of lime in order to produce workable and sturdy products.
Having thrown the reputation of his company down the pan, after producing a wealth of glass and crystal products that crizzled over time, Ravencroft eventually discovered that by adding lead oxide he could stabilise the mixture. But more than that, the addition of the lead oxide gave the glass a sparkling and almost magical quality.
We know now that is because the inclusion of PbO increases the refractive index of the material. A higher refractive index means that the light is more likely to encounter ‘dispersion’, where the white light is split into its component colours, which is why we see the glinting and sparkling of such glass.
But it wasn’t just the decorative qualities that made lead glass so popular. The addition of lead oxide also lowered the working temperature of the glass as well as its viscosity. This means that it was easier and more energy efficient to work with, whilst the lower viscosity meant that you were less likely to end up with air bubbles trapped within your finished product.
Everything was all well and good and people were making decanters out of the stuff, glasses, tumblers. We were rejoicing at the innovation of lead glass, until, that was, we discovered that lead is actually poisonous and we shouldn’t really be making things out of it - not least things that we consume from.
Instead what we now see are ‘lead glass’ or ‘lead crystal’ products that are in actual fact made with zinc oxide or barium oxide. With a similar refractive index and low working temperature, they are just as effective and work just as well as decorative glassware pieces.
The inclusion of lead glass is something that I, myself, am particularly fond of in regards to internal doors and windows. Used as a trim, or even as a panel in the door unit, its sparkling quality can look truly beautiful and give a real dynamic look to the room.