Black glass or jet?

There is a popular misconception that 'jet' is simply black glass. However, it refers to a completely different material, which was extremely popular in Victorian times, during the queen's mourning. The fact that black glass buttons became extremely fashionable is just because they were a cheaper substitute for the genuine jet buttons worn by the queen Victoria herself after the death of her husband. Polished jet looks so similar to black glass that it is difficult to tell the difference at first. However, there are a few details that can help us tell them apart.

Tiny jet buttons

Jet is a mineral, a stone, which means, these buttons are not cast, like glass buttons, but cut and then shaped, ground, polished etc. using some milling machinery. If they have a self shank, it is made from the same piece and is always seamless...



Black glass buttons from the Victorian times usually have metal shanks. Only in the twentieth century did they start to be manufactured with molded self shanks. There were different kinds of shanks used in the process. The oldest include shank plates over, what was called, swirl backs. It was part of the manufacturing process. 

A box shank also indicates that a button is older. This black button is from ca. 1920s the latest. 

The surface of a jet button can be polished smoothly, which is when they resemble the shiny glass buttons most. However, jet buttons can have mat finish, which is not likely to be achieved on glass. 

These jet buttons have carvings that make them look as if made of woven leather. 

Jet is very brittle. So is glass - you will say. Nevertheless, they break and get damaged in different ways. Glass is likely to produce chipping and crazing. Jet just breaks in two or more pieces. The chippings are more as if indented. Crazing is unlikely. 

Crazing is what happens to the glass buttons with age. These wrinkles are tiny cracks on the surface, but the piece still holds together. This does not happen to jet buttons, as they would have already broken apart.

Many say that the easiest way to tell is by weight, as jet is lighter than glass. I have heard suggestions that jet will float on water (!?), then, that it would float but only in seawater. Well, I haven't tried it with sea water, but it did sink in a glass of tap water. 

The difference between jet and black glass is quite difficult to perceive, but I think that with naked eye and some experience we will be able to tell jet from glass without risking losing a button on the seabed. 

Lacy pattern on a vintage glass button: this is an example of Victorian times design.
Instead of mat finish we can see a very fine texture on its surface.