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Some unusual translucent green in a Venetian 6 layer chevron
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Posted by: Carl Dreibelbis

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08/29/2009, 13:14:41

Huh? Ok, I never saw this translucent green until I photographed the bead. Any comments are welcomed. Thanks.

Carl

I know I'm wrong but...
Re: Some unusual translucent green in a Venetian 6 layer chevron -- Carl Dreibelbis	Post Reply	Edit		Forum	Where am I?

Posted by: TASART

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08/29/2009, 13:49:41

It almost looks like they used the same mix of two types of glass you find in the older greenhearts! Cool bead, you been holdin' out again!

Good observation......right or wrong
Re: I know I'm wrong but... -- TASART	Post Reply	Edit		Forum	Where am I?

Posted by: Carl Dreibelbis

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08/29/2009, 14:20:10

Colorant Failure
Re: Some unusual translucent green in a Venetian 6 layer chevron -- Carl Dreibelbis	Post Reply	Edit		Forum	Where am I?

Posted by: Beadman

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08/29/2009, 18:41:53

Hi Carl,

Coincidently, I almost mentioned this in my previous post to you.

Another thing that happens to copper-red glass, with some frequency, is that the copper emulsion fails and does not color the glass red in-part. Instead, the glass reverts back to it's natural green color (the base glass being uncolored and nondecolorized greenish glass, naturally colored by iron that is present in the sand when the material is batched).

I asked Art to explain this to me a few years ago, but his explanation was not helpful. I said I thought the batch had areas where the colorant was absent, or had reverted to neutral. He said it happens because the glass is "tortured" to become red, and that at places where it's green the copper is present, but not providing a red color.

In any event, MANY brick-red glass beads show structural lines or rings, that appear black. If you can get some light through them, you can see they are green.

So, Thomas is not incorrect, exactly. The base glass for green-heart beads is uncolored/nondecolorized green glass—varying from pale or yellowish green to saturated green (depending upon how much natural iron is present).

I have documented a number of chevron beads that display their red glass reverting to green. It's not common, but it's not unheard-of. And it's totally accidental.

Jamey

Great information Mr. Allen!
Re: Colorant Failure -- Beadman	Post Reply	Edit		Forum	Where am I?

Posted by: Carl Dreibelbis

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08/29/2009, 18:51:57

Hi Jamey,

Makes perfect sense. Thanks again for all of your good input.

Carl

would that explain this bead
Re: Colorant Failure -- Beadman	Post Reply	Edit		Forum	Where am I?

Posted by: TASART

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08/29/2009, 22:17:54

or is this a bead intentionally made in this combo, do you think?

Your beads catch my eyes again and again...............
Re: would that explain this bead -- TASART	Post Reply	Edit		Forum	Where am I?

Posted by: freedomgood

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08/30/2009, 04:00:37

Very likely it's intentional with this one.
Re: would that explain this bead -- TASART	Post Reply	Edit		Forum	Where am I?

Posted by: Beadman

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08/30/2009, 04:02:25

When my new scanner is up and going, I'll try to scan some "accidents."

Jamey

Re: Colorant Failure in chevron brick red glass- Perhaps this will be more helpful Jamey
Re: Colorant Failure -- Beadman	Post Reply	Edit		Forum	Where am I?

Posted by: Art

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09/04/2009, 10:57:35

The reason the red (hematinone ) glass is red to the eye is that at a microscopic level there are a bajillion tiny crystals of red copper oxide suspended in the glass. These crystals grow in a condition which is akin to torture for the glass where it its held at a relatively low temperature with a super saturated copper content in an oxygen starved atmosphere in the furnace. A variation of this process is used to make aventurine. The growth of these crystals takes time. Aventurine glass will likewise appear green if the crystals are cooked out of it. so care must be taken to keep it from becoming too hot in design application after the crystal growth has been done. The green in the glass is a function of the red copper oxide crystals going non crystaline and reverting to copper green. It would provide identical chemical analysis if a spectrographic analysis were done. The red glass in question would rather be green, but is red to the eye due to the red copper oxide crystals being present in mega numbers. The crystals are flat plate like structures which align themselves much as a pile of paper would if thrown on a table. All those tiny flat plate like crystals pile up and create a red opaque look to the glass. If you slice any of that brick red copper glass thin enough it will appear green. Many of the older chevrons have green striations in the red layers giving rise to much discussion over how many layers are in the bead. These questions arise with fair frequency on this forum. Without question when you see those dark striations associated with the brick red it is a function of the red degenerating from its suspended red copper oxide crystal state to a more relaxed copper green. The bead shown in this thread presents an interesting view into this phenomenon. With modern industrial methods giving greater control to temperature and atmosphere, modern glass makers have been able to keep better control of this type of red so that one sees this effect rarely in the newer beads.
The book Colored Glasses by Woldemar Weyl published by the Society for Glass Researchers in England can provide much information on glass colorants at a very scientific level. It's a fairly obscure book printed in 1951 and is long out of print.
Hope that this clears some of this up for you.
best,
art

Modified by Art at Fri, Sep 04, 2009, 11:03:34

Thank you so much for this illuminating explanation :-) . !!
Re: Re: Colorant Failure in chevron brick red glass- Perhaps this will be more helpful Jamey -- Art	Post Reply	Edit		Forum	Where am I?

Posted by: Snap

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09/04/2009, 20:14:57

"Aventurine glass will likewise appear green if the crystals are cooked out of it"
Re: Re: Colorant Failure in chevron brick red glass- Perhaps this will be more helpful Jamey -- Art	Post Reply	Edit		Forum	Where am I?

Posted by: Joyce

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09/05/2009, 09:23:17

Thanks Art! That's all helpful info. And I've wondered more than once why aventurine that's not all that sparkly sometimes has a slight greenish tint to it.

I always wondered why aventurine GLASS & aventurine STONE were so different!
Re: "Aventurine glass will likewise appear green if the crystals are cooked out of it" -- Joyce	Post Reply	Edit		Forum	Where am I?

Posted by: Luann Udell

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09/05/2009, 09:53:06

I always thought it was odd that two such different materials were called by the same name. At least they have (sometimes) "green" in common! :^)

Luann Udell artist & writer Ancient stories retold in modern artifacts LuannUdell.com
Related link: Aventurine glass vs. stone

Avventurina and Goldstone
Re: I always wondered why aventurine GLASS & aventurine STONE were so different! -- Luann Udell	Post Reply	Edit		Forum	Where am I?

Posted by: Beadman

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09/06/2009, 15:52:44

Hi Luann,

I can't entirely agree with the Wiki exposition.

I do agree (to my knowledge) that the quartzite mineral is named for the glass—and I agree that this is a really unusual occurrence (it usually being the opposite situation). You can look at avventurina glass and aventurine quartzite (as we know it from India), and see how they are different, or how they are alike. They have much in-common. As it happens, in the modern bead world we see a lot more green aventurine quartzite, and a lot of brown/golden avventurina glass. However, there is also a brown/golden (sometimes characterized as "red"—though it's not red) aventurine quartzite. And if this is what you were familiar with the comparison would be easier to make. The mica inclusions in quartzite are essentially white and non-metallic-looking, versus the coppery-red tone of the glass—but effect provided in both materials is reasonably similar.

A BIG problem with the essay at Wiki is that it's filed under "Goldstone (Gemstone)"—which is very misleading. The monologue were better placed under "Avventurina Glass," with a mention of goldstone glass as a subsidiary. The author has a limited knowledge-base and understanding of the larger picture; and I would guess doesn't know much about glassworking.

At Venice and elsewhere, the greatest proportion of beads that feature avventurina glass have been hot-worked (usually lampworked, but also enamelled). Sensibly, the class of glass is better named "Avventurina." It is ONLY when the glass has been lapidary-worked, like a mineral, that it is characterized as "goldstone." This distinction was respected by bead sellers (and some collectors) up until the 1980s, by which time apparently the distinction between them had become lost and/or was ignored or misunderstood (I say based on my observation).

Another curious thing is that MANY people insist that there is a mineral called "goldstone," that the glass imitates. I have even been told this by Gemological Institute of America (GIA) graduates! This is totally inaccurate. There are TWO minerals that resemble goldstone/Avventurina—these being the quartzite already mentioned, and another mineral called "sunstone," that is a variety of feldspar. Sunstone reentered the marketplace a few years ago, after being reasonably unheard-of (in my experience)—it being the State Stone of Oregon, and that's where it's easiest to find specimens—until recently when commercial quantities were again available and now made into various products, including beads. sunstone is typically golden colored, with a metallic Sheen (in the better more-desirable specimens), and bares a decent resemblance to goldstone. However, many specimens are essentially clear and colorless, with very few inclusions, and hardly warrant being called "sunstone."

Jamey

Related link: http://en.wikipedia.org/wiki/Aventurine

Sunstone
Re: Avventurina and Goldstone -- Beadman	Post Reply	Edit		Forum	Where am I?

Posted by: Beadman

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09/06/2009, 16:18:38

Related link: http://en.wikipedia.org/wiki/Sunstone

Jamey, you could correct & rewrite the Wiki entry!
Re: Avventurina and Goldstone -- Beadman	Post Reply	Edit		Forum	Where am I?

Posted by: Luann Udell

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09/06/2009, 16:37:15

Can't think of a more knowledgeable or more qualified person to do it....

Thank you for following the train of thought to its conclusion so clearly--that was hugely helpful! :^)

Luann Udell artist & writer Ancient stories retold in modern artifacts LuannUdell.com

This green has nothing to do with base glass or iron present
Re: Colorant Failure -- Beadman	Post Reply	Edit		Forum	Where am I?

Posted by: Art

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09/04/2009, 11:00:33

See my followup post above

Modified by Art at Fri, Sep 04, 2009, 11:02:29

Oxblood red sample photos....
Re: This green has nothing to do with base glass or iron present -- Art	Post Reply	Edit		Forum	Where am I?

Posted by: brian graham

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09/06/2009, 09:03:28

Here's some copper opaque red I melted last year which shows the red and green in the same piece of glass - there is also some copper aventurine.
All of the photos below are from the same glass batch.

www.briangrahamglass.com

Observations on iron that I forgot to mention.....
Re: Oxblood red sample photos.... -- brian graham	Post Reply	Edit		Forum	Where am I?

Posted by: brian graham

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09/06/2009, 09:50:48

Some of my observations on iron. All of my opaque red glass has a high percentage of iron in it. Every old opaque red recipe that I have observed includes a high ammount of red iron oxide - crocus martis is what they refer to it as - see Antonio Neri, "The Art of Glass" - 1612. I would like to try to melt the opaque red again without the added iron.....another project on the back burner..lol

The same glass recipe results shown above if melted in a neutral or oxidising atmosphere (as oppose to a reducing one) would be a dark green transparent color - ranging closer to an emerald through celadon color than compared to an olive shade. I have samples at my shop but not at home or else I would show a pic...sorry. It essentially looks like the green shown in the opaque red above except there is not a trace of the red opaque.

With no iron present, the color would just be transparent turquoise. It is my opinion that iron would seem to have to be present in order for the darker green color to be achieved. Here is what a typical ionic copper color looks like. The pic below is pretty much completely iron free. I have melted copper blue many times and the results are always the same - maybe a little bit darker blue than shown in my photo but definitely not green. Disregard the bottom image...

www.briangrahamglass.com

Thanks Brian! I will have more to say about this another time.
Re: Observations on iron that I forgot to mention..... -- brian graham	Post Reply	Edit		Forum	Where am I?

Posted by: Beadman

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09/06/2009, 15:55:53

Welcome glass melter Brian!
Re: Observations on iron that I forgot to mention..... -- brian graham	Post Reply	Edit		Forum	Where am I?

Posted by: Art

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09/07/2009, 10:58:00

Nice post Brian, It's good to see other glass melters out there doing experimental work and interested in beads too. We always had chrome in our green glass-the ratio of the copper /chrome analog varying the shades of green. I don't recall that we included iron in our green batches but it's possible. My days with batch melting are long ago. Iron was surely present in all the older glasses to a greater rather than lesser degree due to materials refinement issues. I've don't recall reading of iron content being a factor in aventurine or hematinone development but could see where it might play a part. I haven't had the chance to obtain or read the Neri treatise and since you've read it I expect that you are more informed on Italian practice than I on the matter. I've seen iron reds in pottery glazes and in some glass. Your copper blue is an excellent presentation of a pure copper blue. I made an attempt at copper aventurine once with very similar results to the pics you showed, but you got better sparkly than I did. Mine was marbly as well with green and red present. It was a one time experiment. We did make chrome green aventurine on occasion and it's much more direct and easier to get the crystal formation in that glass than the copper version. The green aventurine seemed much more stable at working temperature too. I no longer melt much raw batch as it got to be taking up too much time and space and the energy issues are not insignificant.
The biggest point I may have failed to make in my previous post about glass colorants and coloring is that while some common colors are generated by adding a colorant to a base glass ie. manganese purple, copper blue, copper chrome greens,cobalt blue, nickel ambers etc. sophisticated colors in glass notably all the hot colors( reds, yelllows etc. ) are created by very complex conditions created within the glass matrix at an atomic level by subtle chemistry interactions , temperature, time and atmosphere. These colors aren't made by adding a colorant to a base glass akin to adding food color to water.
What kind of glass objects do you make? Do you have a website? or a link to pics of your work?
Here's to more and better glass in beads and other objects...
art

seymourchevron.com

Great to hear from Brian!
Re: Observations on iron that I forgot to mention..... -- brian graham	Post Reply	Edit		Forum	Where am I?

Posted by: Joyce

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09/07/2009, 13:22:19

Brian is actually one of bcn's earliest "forumites" - I'm always delighted when Brian has posted. I am proud owner of a few of his beautiful glass beads - and remember when he was researching how furnace beads were made using a tapered iron mandrel. I have one of those beads, too!

Here is his new site, link below.

I need to apologize to everyone for not getting the links page updated - so many links are no longer functional. This is due to our personal lives being so dysfunctional over the past year and a half or so - my elderly mom who lived with us for 6 years, now 90, surviving cancer surgery in April of this year, now lives in a home across town. So my days are now spent working almost full time 20 mi. north, trying to help 11 year old Colin with his homework, visiting Mom daily and the usual household duties. More layers of stress as we all have also added, so David and I are not home all that much when we are both awake and aware enough to do web work. I slept for 8 hours last night for the first time in months.

So, I apologize to Brian, Art, Jan, and everybody for being so behind on the links page. I do have everyone's new working links in a file for when D. and I can sit down and update it.