Devit - How to Prevent It & How to Fix It.
What is Devitrification?
Devitrification or Devit as it is commonly known, is difficult to recognize. It is a scum-like whitish discoloring which sometimes appears on the surface of your glass - usually is the most objectionable place on the piece you are fusing.
When devit occurs, molecules in the glass alter their structure into that of crystalline solids. While there are many detailed technical explanations for what actually happens on the molecular level, I will skip them in favor of providing some guidance in what you can do to prevent devit and what you can do to remove it if rears its ugly head,
Some factors surrounding the occurrence of devit are under control of the artist. Devit can occur when holding glass at a high temperature too long. It can be caused by the existence of any foreign residue on the surface of the glass. The chemical composition of the glass has an impact. Darker more opaque glasses require more chemicals and are more prone to devit while clear or cathedral glass is less prone.
There are many ways to minimize the probability of devit. The following paragraphs suggest steps you can take to minimize it.
* Clean and then re-clean any glass that is going into your kiln. Specs of dirt, dust from grinding, oil from your skin; all of these can cause nucleation points where devit will have a tendency to occur. Cleanliness is probably the one characteristic that the artist has most control over. I soak the cut or ground glass as soon as I have a piece ready for the assembly stage. This soaking allows the edges of the piece to be cleaned easier and more thoroughly..
* Keep your kiln clean. You don’t want to put clean glass into a dirty or dusty kiln. I vacuum my kiln thoroughly before every firing. Making sure you aren’t getting tiny bits of debris or ‘kiln-snow’ when you close the lid of your kiln. If so, you may need to use some kiln cement on the roof of your kiln. If you use Thinfire or any type of shelf paper, you should be aware that it has a tendency to curl around the edges at high temperature and that it turns to a very fine powder. As your kiln is heating, there all types of air convections being created moving dust and debris around inside the kiln so cleanliness is really important.
* To the extent that your design and firing schedule allows it, limit the time your glass spends at a high temperature. Different glasses and different colors react differently but you can expect to be promoting devit when you keep dark, opaque, Bullseye glass at 1450 degrees for an extended period of time. Check with the manufacturer of the glass. They should be able to give you guidance regarding what to expect with their products. If you are uncertain, run a test. If you don’t develop devit with your test remember that it is not a guarantee. Glass is fickle.
* You can use a devit spray which is basically Borax and water. There are several web sites that will provide you with the menu and it is very simple to make. The problem is that the devit spray adds another layer to your glass and changes the appearance – better to some and not so great to others.
My personal approach is that I do everything I can to eliminate devit through cleanliness but I do not sacrifice my design considerations. If my work has devit when it comes out of the kiln; that is what I have a sandblaster for.
Devit can easily be removed with a sandblaster. I use 120 grit Aluminum Oxide abrasive in my blaster if I am removing devit. Then the piece goes back into the kiln to be fire polished – at well below any temperature that would encourage devit.
Living with devit is a part of working with glass, just like sharp edges.