View Full Version : Reducing Glass

Art Ciccotti
04-17-2012, 04:02 PM
I have a couple of questions about the glass that has the properties of reducing. I have been using it for years but never really understood how it works... What actually occurs on the surface of the glass to cause the metallic look? How is the reduction best achieved when in the glory hole. What causes the browning out effect? Thank you in advance for the information on this subject.
Art Ciccotti

Cecil McKenzie
04-17-2012, 10:43 PM
Here is a video about oxidation reduction reactions.

I f you read the notes it explains that when something loses an electron it is oxidized and when it is reduced it gains an electron or electrons.

Take iron. When it rusts it is oxidized. So the iron loses an electron or two or three to oxygen. In doing so it changes to red iron oxide or I think also yellow iron oxide. Now if you take that iron oxide and heat it and put it in the presence of something that has more affinity for the oxygen ( like a carbon rich fuel) then the oxygen moves to combine with the free carbon in the reducing flame.When the oxygen moves away from the iron oxide the iron gains electrons and reverts to its elemental state of being iron. I am not sure if this reaction happens in glass but it is the reaction in the process of making iron from iron ore (oxides or iron ). Iron ore is heated in the presence of coke or charcoal and liquid iron or steel is the result.

Silver and copper are two elements that manifest oxidation reduction reactions on the surface of glass. Blue glass based on copper manifests an oxidized state when put in a reducing atmosphere the copper gains electrons and is reduced to the elemental state which is copperery red.

Silver is another reactive color which when reduced enough will appear like a mirror on the surface. The variety of colors attainable from silver may reflect different levels of reduction because the silver can have different oxidized states and there might be some physics involved in thin layering of the reduced states on the surface.

I think that some of the mirroring on color bar colors is reduction of the lead in the glass by the same process gaining electrons from a reducing atmosphere.

I hope I am basically correct on this and that it helps a little.

Pete VanderLaan
04-18-2012, 02:29 AM
A. Reducing agent takes something away from another element or compound. "Reducing it ". A hydrocarbon rich gloryhole atmosphere seeks equilibrium and can reduce a silver or copper rich glass taking from it oxygen to support the equilibrium exchange. It leaves the pure metal which in some instances takes the oxygen back
usually from open air.

Your glass is chock full of O2. Try sometime hitting a gather with cold compressed air for 30 seconds and take it away. See what happens.

Tom Clifton
04-18-2012, 12:54 PM
And though I have not tried it yet, fusers say that you can reduce silver glasses in an electric kiln by putting a pea sized lump of charcoal in the kiln along with the objects being fused. (Usually small pendants etc...)

Pete VanderLaan
04-18-2012, 04:43 PM
Reducing in an electric kiln can be done that way chunks of wood will do it as well but its hard on the elements

Pringle Teetor
04-18-2012, 10:48 PM
@ Pete ... BUBBLES!

Tom Clifton
04-19-2012, 09:23 AM
Reducing in an electric kiln can be done... but its hard on the elements

Only in that it reduces the oxide on the elements as well as the oxides in the glass. Another subject for study...

Pete VanderLaan
04-19-2012, 02:17 PM
Well that's like saying "only that " fluorine dissolves elements. Anything shortening your equipment life is a cost of doing business. If you don't mind the consequences, that's fine, it's just that many people are unaware of the consequences since the schools have gotten to be as poorly focused as they are.

Tom Clifton
04-19-2012, 04:52 PM
Anything shortening your equipment life is a cost of doing business.

Score: Pete 1 Tom 0

BTW, I went by HiTemp today and bought some IFB. Gave Tom regards from you. He says he really appreciates all the referrals. I told him I was instructed not to mention horse shoes and he just smiled...

Pete VanderLaan
04-20-2012, 01:59 AM
You're lucky you got out alive without a lecture on the history of throwing shoes. As I have noted in the past, "Close " only counts in horseshoes and atomic bombs.

There are some suppliers well worth having in you rolodex. Tom is one of them.

Art Ciccotti
04-20-2012, 05:49 PM
Ok so in practicle application when I am going for the reduction effect on say silver amythyst the glass has to be hot enough to remove the O2 from the surface when in the reducing atmosphere of a glory hole (hydrocarbon rich atmosphere). So the idea then is to pass the glass into the glory hole with air turned down observe the metallic effect or color change then pull out. I know this sounds basic but I have experienced a "burned out" effect look on the surface in times past. Related to that is it possible to return glass back to a metallic state once burned out? So I am trying to figure out the pattern as to why it happens sometimes and not others, and how to prevent it. Also I have noticed that when going for the reducing effect I have to run the piece in the face of the flame, pull it out for a few seconds then go back in to bring out the even luster on the glass. So what I am getting to is that it appears to also need a certain temperature to obtain the full reduction so that in a sense by going in and out of the glory hole this adjusts the temperature. Possibly this is what Cecle was talking about with the different states of oxidation or coloration on the same surface. The partail reduction on some of the frit would appear to have halo rings. BTW thanks for the video Cecil. You know Pete when you mentioned blowing cold air on the surface I have noticed that there were times when papering the glass there would be a momentary sort of reduction effect. I will have to try the compressed air thing next time I get out in the studio. Hope my questions makes sense? Thanks again for the input everyone.

Pete VanderLaan
04-21-2012, 12:55 AM
When a glass plates out the metal in guestion is usually copper or silver which do have slightly different bonds,, or to look at it a slightly different way- How easily is the metal in question going to let go of that single oxygen in order to be "reduced?" Mottling on the surface of the glass tells you graphically that glass has an irregular matrix. You are also getting to see that both heat and a hydrocarbon rich atmosphere affect that reduction effect. Finally you are seeing part of the surface re-oxidize when you pull out of the gloryhole. I don't know if you are familiar with the term "Redox" but it is cyclic reduction/oxidation.

Anyone with any experience in glass knows that some colors plate out better than others. A nice unstable glass usually plates out well. Kugler gold braun was a glass of choice for me during the brief time I used German rod.I pay zero attention to other peoples colors these days so I am no help there.

And yes, you can reduce too long and burn a Color out. Once those colors start to put their energy into making colloidal strands, they don't reduce well at all. You can seal a reduced surface quite well with a good stannous fume.