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Tips, Techniques, and Questions -- Technical questions or tips |
2009-01-30, 10:47am
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Roo ...
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Location: Minnesota
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Reducing Over Encasement?
I've seen mention of reducing a silver glass that has already been encased. This would seem pointless to me, but I saw it in Val Cox's frit book (she said she would elaborate in the section on Faux Boro but I couldn't find anything further on it there), and someone also posted in LWE recently (I *think* it was in the SE 4 Exchange, but I'll be darned if I can find it today), where the artist reduced the silver glass, encased, and then lightly reduced again afterwards.
What exactly is supposed to happen when this is done? Does it affect the silver glass even though the silver glass is completely covered with clear? I'd love some further description of what this technique does (I've tried it but it was very uneventful!). Mystery to me!
Any help appreciated!
- Becky in MN
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2009-01-30, 11:58am
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Hmpf. I'm with you.... unless there is some silver glass peeking out one of the ends and you are essentially fuming the clear encasement (and making it oh-so-shiny!) with that little bit of exposed glass??
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"In theory, there is no difference between theory and practice; in practice there is." ~ Chuck Reid
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2009-01-30, 12:32pm
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I think that the second 'reduction' is more likely to be developing a striking color in the encased glass through temperature change rather than reducing it. That's my take on it, anyway.
Robert
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2009-01-30, 2:42pm
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Born Facing Left
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You can reduce silver glass before it's encased, not after. Some silver glasses will keep their reduction effects under encasement, some, not so much.
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Sherry
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2009-01-30, 3:12pm
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da General
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Karolen / sunflower33 posted this in SE3 - she was able to reduce Elektra after encasing it.
http://www.lampworketc.com/forums/sh...&postcount=680
I haven't tried it tho!
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Hayley
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2009-01-30, 3:26pm
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Born Facing Left
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Quote:
Originally Posted by Hayley
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That's incredibly cool, I just don't understand how it's possible? That's one lovely bead!
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Sherry
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2009-01-30, 4:10pm
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Its possible because the temperature change will bring certain metals to the surface. I just had a discusssion with Abe about this and I have done it too. eta think about how boro works. A lot of it is encased and then struck in the flame or the kiln to develop color.
Paula
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2009-01-30, 4:33pm
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Therein lies a difference between (1) striking color with heat changes and (2) reduction of a surface by removal of oxygen from metal oxide by the fuel gas. They're different processes but the words are often used interchangeably.
Robert
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2009-01-30, 4:37pm
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Quote:
Originally Posted by PaulaD
Its possible because the temperature change will bring certain metals to the surface. I just had a discusssion with Abe about this and I have done it too. eta think about how boro works. A lot of it is encased and then struck in the flame or the kiln to develop color.
Paula
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Remember that striking and reduction are two completely different critters. Striking is a function of temperature and reduction is a function of flame chemistry. It's completely possible to strike encased glass, but reducing encased glass just doesn't figure... there's no way to affect the "atmosphere" of encased glass.
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2009-01-30, 4:38pm
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Heheh, GMTA, Robert!
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So come up to the lab and see what's on the slab...
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2009-01-30, 4:56pm
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Roo ...
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Quote:
Originally Posted by prairieson
Remember that striking and reduction are two completely different critters. Striking is a function of temperature and reduction is a function of flame chemistry. It's completely possible to strike encased glass, but reducing encased glass just doesn't figure... there's no way to affect the "atmosphere" of encased glass.
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I'm understanding this, which is why I am confused why the word "reduce" is being used instead of "strike" when I've seen this described (by knowledgeable folks). It hadn't occurred to me that the usage was getting turned around -- which, now that I think about it, is entirely possible.
But if this DID work, I would sure like to know more about it!
Regards,
- Beck.
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2009-01-30, 5:16pm
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The end result of the two processes is the same. Metals are brought to the surface.
Some boro boys often call what we soft glass workers refer to as reducing (no oxygen), striking.
I have done both processes with encased glass although it's a slower process once the glass is encased..
Paula
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2009-01-30, 5:29pm
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Roo ...
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Quote:
Originally Posted by PaulaD
The end result of the two processes is the same. Metals are brought to the surface.
Some boro boys often call what we soft glass workers refer to as reducing (no oxygen), striking.
I have done both processes with encased glass although it's a slower process once the glass is encased..
Paula
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So, Paula, does this result in reduction on the surface of the clear encasement, or does it change the appearance of the interior silver glass (independent of any striking)? I'm still not clear what the end result should/could be.
Thanks!
- Beck in frickin freezin MN
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2009-01-30, 5:54pm
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Quote:
Originally Posted by PaulaD
The end result of the two processes is the same. Metals are brought to the surface.
Some boro boys often call what we soft glass workers refer to as reducing (no oxygen), striking.
I have done both processes with encased glass although it's a slower process once the glass is encased..
Paula
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The end results are quite different. When reducing, the metals are coaxed out of their oxide state so as to create a metallic luster on the surface of the glass. When striking, the metal oxide matrices are "grown" and "collapsed" so as to create colors within the glass, not just on the surface.
Some colors will reduce and not strike, Reichenbach Iris Black comes to mind. Some will strike and not reduce. Some will do both. But in order to reduce, the glass must be exposed to the flame so as to allow the reduction process to take place. That simply can't happen if the glass to be reduced is encased.
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2009-01-30, 6:08pm
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Quote:
Originally Posted by prairieson
The end results are quite different. When reducing, the metals are coaxed out of their oxide state so as to create a metallic luster on the surface of the glass. When striking, the metal oxide matrices are "grown" and "collapsed" so as to create colors within the glass, not just on the surface.
Some colors will reduce and not strike, Reichenbach Iris Black comes to mind. Some will strike and not reduce. Some will do both. But in order to reduce, the glass must be exposed to the flame so as to allow the reduction process to take place. That simply can't happen if the glass to be reduced is encased.
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There is new research out that disputes and redefines this process as well as the classic definitions. You may want to read Jesse Kohl's recent research and his publications. Since he is a chemist his reading is much more interesting than my interpretations. I've decided that I'd rather go light my torch tonight than spend my night typing about glass chemistry.
See you later!!
Paula
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2009-01-30, 7:53pm
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Lover of all things color
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This all makes sense to me and I had a bit of experience with the reduce, encase and then strike theory. I reduced Triton to it's metallic sheen, encased to get a beautiful bright blue, as I was reheating to melt down and smooth out all of the clear the bright blue slowly turned to a lighter teal color. I assume this is the further striking of the silver glass to a lighter color. I was slightly disappointed with the results as all I wanted to do was cover the reduction to protect and enhance it. Lessons learned.
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2009-01-30, 10:26pm
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Actually, none of this makes sense to me, and I'm slightly confused. To me, reduction is a surface effect, typically caused by high fuel/low oxygen flame chemistry which brings metals to the surface of the glass resulting in a lustrous or metallic surface.
When I think of striking, I think of internal color changes caused by cooling/reheating/crystal growth, etc.....I've always thought that it was a heat effect as opposed to a fuel/surface effect.
I'm fairly confident in my knowledge in terms of how I use the glass, but I'm interested to find out that my assumptions may have been wrong. I still fail to understand, however, how a surface reduction effect could possibly be achieved under a layer of encasement that seals out the flame. I think that changes in a reduced surface after encasing are likely not striking, but are just the lessening of the appearance of the reduced surface, possibly due to the unavoidable presence of oxygen in the flame while encasing, not to mention the effect of viewing the surface through a layer of transparent glass.
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2009-01-31, 8:41am
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You are mostly correct in your assumptions.
Reduction (as we call it) is a surface effect resulting from the removal of oxygen atoms from metal oxides in the glass. Reduction surfaces are, as a rule, no more than a few microns (micrometers) thick at the most. Colors on reduction surfaces result from the composition, size, shape and thickness of the metal particles in the surface layer. The color does not necessarily indicate the metal involved, i.e. gold sheen isn't necessarily elemental gold on the glass.
Striking is a different process that takes place beneath the surface and can include much thicker layers within the glass, up to the entire thickness of the piece. Color changes result from the rearrangement of electons in the glass matrix under the influence of heat energy. While these changes might be considered changes in redox potential in a technical sense, it is not reduction as we tend to rrefer to it. You can see stiking reactions beneath encasement of reduction glass that occur due to heat changes and interaction with glass components that are isolated from the flame.
Robert
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2009-01-31, 12:52pm
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Not that it applies directly to the glass in question, but Bullseye has a "reactive" clear that reduced the glass that it is in contact with. They have a reactive white as well, but it's harder to see the effects.
I don't really understand the chemistry of it, how you can make a glass that removes electrons from the glass around it, but it works.
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2009-02-01, 8:51am
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All of that heat energy from the flame makes all sorts of exotic chemistry possible. Electrons are promiscuous little buggers when they get excited.
Robert
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2009-02-01, 9:14am
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yeah i second what mr. Simmons explained multiple times. Reduction and striking are two completely different things...Striking refers to crystal growth while reductuion refers to drawing metal ozides to the surface of the glass...If something is encased in clear...then a reduction flame will draw no metal oxides from that clear because there are none in clear.
There are hundreds of articles about this stuff all over the internet.
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2009-02-01, 10:07am
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Caveat: Clear can do strange things if you use one of the 'lead crystal' clear glasses. The lead oxide gives you a higher refractive index and clear lead glass becomes 'crystal' when cut and polished. You can surface reduce this glass, but all it'll do for (to) you is put a metallic sheen on the surface that obscures whatever has been encased.
Robert
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