While walking along the canal to photograph Galton Bridge, just across from the Chance Brothers site, I came across a scattering of stones, of a sort I’ve seen before in a number of places, mostly archaeological iron-working areas. I’ve always previously thought they were reject glass, a kind of glass-slag.
After cleaning a few and doing some basic-level research I find they are what is known as either slag-glass or agate-glass. The material is a combination of the minerals cryolite and manganese and, what is probably the main material here, iron ore slag, ground to a powder, which produces a colourful vitreous material, which clearly shows its flow paths, bubbles, and areas where it has come into contact with other materials. The addition of other minerals brings other colours. During the early twentieth century a similar-looking kind of glass was made into lampshades, bowls and vases, and some jewellery, mostly in the north-east of England and in the US. The material used in this case is also known as slag-glass or agate-glass and comes in a variety of colours; look it up on ebay, and you’ll see the range of products made from it. Check out Tiffany lampshades which used it a lot. In a way the organic flow shapes are equally attractive; they remind me of lava flows, and tectites, the vitrified tear-shaped bombs produced by meteorite impacts.
So, what to do with this wonderful stuff? I propose to lead an expedition next Friday (3rd June) to collect some more, and to spend some of the Saturday session photographing it, to be made up either into a little book, or a small photographic exhibition, or both. I had also thought about the possibility of a local glass-worker making something with it – maybe panels, plates, windows, bowls – but Peter Knowles reckons that it would need a melt temperature of between 1200 and 1500 degrees centigrade. A more viable path would be carving it – again I’ve found some examples of this on the internet; but there is the danger of its shattering. Experiments will show what happens.