104 Viscosity, anyone?

[glassbead]

Before you begin- Lauscha has, over the last couple of years, reformulated their glass to work better with Moretti. But I still feel this information is excellent and relevant for other reasons. I had to come back and read it today myself after all this time. Just got some very old Lauscha, and needed to refresh my memory.

This is driving me crazy. Does anyone know if there is a way to use glass that has a different viscosity to safely make a bead? How do you find out what the viscosity is? Does annealing at a higher temperature take care of it? I use all kinds of Moretti, Vetrofond, and Kugler with Lauscha clear. They are all meant to have a 104 coe, but sometimes bad things happen. I particularly wonder about the Lauscha and ASK104 colors. I've gotten to the point that I won't use them together. Of course I'd like to be able to. It seems that viscosity difference is the key, but can it be overcome?
I got an email from Frank at Glass Daddy that helped, so I'm adding it here (he said it was ok, as long as I mention that some of his information came from elsewhere), but it is hard to cross reference all of the available 104 glass for all the variables- or is there a place to find this that I don't know about?

If anyone has an answer, or part of one, I'd appreciate it greatly!
Thanks,
Laurie

Ok, so here is the information I was emailed by Frank at Glass Daddy about the Lauscha glass:

The COE on clear and the transparents is shown by the factory to be in the range 102 to 105, and the opaques a little higher at 108 to 110.

Here is some data that I copied from their site.

Color Normal opaque Normal Clear
COE 108-110 102-105
Transformation Point 450 C 530 C 986F


You might notice also that the transformation temperature, that would be used in annealing the glass is higher than the 950 degrees that many people use with the moretti.

One last point about the glass is that the clear is more viscous than the moretti at the same temperature.

I'm not a glass artist myself, but from what I have been able to learn from those who are, there are several factors that are important in avoiding thermal and incompatibility cracks.

The annealing temperature needs to be high enough to relieve the stresses that are present in the glass right after working it; I don't think 950 is high enough. Also, some people let the finished bead cool till it loses the red glow before putting it into the kiln; with lauscha glass it is best to let the bead firm up outside of the flame, but put it into the kiln while still glowing red.

In a mixed glass bead, the higher viscosity of the Lauscha may set up stresses with the lower viscosity glass on cooling, again making the temperature important.

smaller beads are less subject to problems than larger ones, as the larger ones may have different temperatures in different parts of the bead that result from the bead being in and out of the flame. You mention the lauscha red as being a problem; that may be due to the bead coming out of the flame to cool enough to make it strike to the red color when it is put back in the flame.

And finally, the hothead may not be able to keep larger beads hot enough to be a uniform high temperature, and if your kiln is not hot enough to relieve the stresses that might be part of the answer.

I only deal in Lauscha, so cannot speak for the other manufacturers, and I think the best place to find out what others can contribute might be the Wet Canvas web site where people are very helpful and willing to share their knowledge.

Hope this helps

[kittyluv4ever]

Hey Laurie,
As far as I know ASK glass absolutely detests being encased with Lauscha as do the silver glasses such as the ones made by Double Helix and R4. I use vetro crystal clear to encase ASK and have not had any problems. I have heard of some people who have had success with Lauscha and silver glasses but for my money the silver glass is just too expensive to take the chance. I don't know the whys and wherefore's of the Lauscha problem I just know lots of people have the same problem. As far as I know there is no way around the incompatibility issue, but maybe someone who knows more than I do will chime in here and help you out.
Best of luck!

[RyanTheNumberImp]

I have never had any problems with different viscosity of glass, black, cobalt blue and lauscha clear are all noticeably stiffer than many of the other 104 colors, while white is extremely soft and there are never any cracking problems between them.

I have never had any cracks because of coefficient of expansion differences either, but I only use 104 and I don't use all that much silver glass.

I actually anneal my soft glass at 1100, I think the kiln may actually be cooler because of the bead door though.

[JetAge Studio]

Glass with different COE are generally considered "incompatable", but as you mentioned, viscosity has a great deal to do with it as well. There really is no way for you to "see" or measure different viscosity, that I know of, without scientific equipment. Certainly there are physical tests you can do, involving polarizing sheets, or to do a compatablility pull test. We all hope that the manufacturers of these glasses know what they are doing, and produce glass that when tested with other "matching" glasses will fit together. There are, however, no worldwide standards of testing to ensure all glasses of a given category will "fit" with one another. So, if your Lauscha does not fit with "x" glass, it just WILL NOT FIT, no matter what you do to it.

I was seeking an answer to this very same question a while back, and asked someone I know who seemed very knowledgeable about the science of glass. He incidently is a retired NASA scientist. Here is an excerpt of my questions, and his responses to helping me understand viscosity. Understanding the behaviour of glass made it easier for me to understand why some glasses, dispite matching COEs just DONT WORK WELL TOGETHER.
I hope this helps....

"COE (linear or volumetric) is not a constant even in one specific glass (or any material)... it varies over different temperature ranges... a COE measurement (when actually done) of a glass from 100 C to 200 C (ratio of change in length or volume) is not exactly the same when done from 150C to 250 C... it's not a real constant for all temperaure ranges or material thckness/size. Still it's 'in the noise' so to say... and accepted as close enough."

Q: So, I still dont understand how viscosity plays more of a role in compatibility than the COE. I also dont understand how some glasses can be stiffer, and still compatible. My main question, simple as it is; what does the term "viscosity" mean?
A: "Viscosity is like 'inch'... just a measurement... in this case think of it like posture - like she has great posture, standing straight and tall, or bad posture, bent over and slumping... and a 'posture judge' assigns a number to the persons posture... 10 good, 8 ok, 5 bad... it's measured in poise (P), each poise number indicating a specifc posture (slouch ) of a glass material. If it's bent (or bends) 'this much', then it's Poise number is X. Then... we take a piece of glass and we go see what temperature 'this much' bend occurs at. And plot all the poise numbers to a specific temperature. If two different glasses follow the same poise-temperature curve... then they are thought to be compatible -- because the internal structure... what the glasses are doing inside themselves... is happening at the same temperature with both... in the same way... expansion, contraction, aligment, whatever it might be... they are for all practical purpose 'the same glass'... they both walk like a duck... even if one looks like a goose."
Q: Does it relate to how a glass returns from a fluid state to solid state? I mean, if two glasses are not compatible, is it because they set up at different rates?
A: "The glass really has no control over rate... we beat the drum... we ramp the temp... it just responds to what we do to it. If the two have different poise curves... if they set up at different temps they would be considered incompatable."

Renee
JetAge Studio

[Tink]

I am SO glad to see this being discussed! And Renee, that's a great bunch of info you've posted. Thank you.

I know Henry has some good info on viscosity on his site. I'll go grab the URL. BRB.... {insert elevator music here} Ok. Here ya go:
http://www.glassalchemyarts.com/support/tech.html

So often, COE is put forth as the "be all, end all" determinant of compatibility. Not so. I'm reminded of an experiment that I worked on with/for a fellow LE glass person: Two glass products. Both TESTED at 104 COE. Explosively incompatible. And it was most likely due primarily to drastically different viscosities.

Anyway, anyone remotely interested in this stuff should read up on viscosity. And now I'm going back to bed.

[glassbead]

Y'all are amazing! I didn't expect such great information, and so quick. At least it makes me feel better knowing it's not just a torch/ me issue. And to know that, indeed, it's a bad idea to encase ASK with Lauscha. I make a lot of beads, but I guess I just don't pay enough attention to what I'm using and what happens when. Actually, until the last year or so, I was a Moretti girl- I don't really like Vetrofond glass, don't ask me why, and I just didn't know about much of anything else. Since I've gotten my kiln, I've expanded what I could do so much, that I guess I just started branching out more. And that's where the trouble began.
Don't get me wrong, I LOVE the kiln. I used to take my beads out of the vermiculite, ream them, freeze them, drop them on the (wooden) floor, and then, if they survived all that and were sculptural or at all large I'd take them somewhere to be batch annealed. All this in an attempt to force breakage if it was going to happen.
Anyway, thanks so much- this is great. I hope more people see it, as I think it explains alot.

[artglass104]

Hi! This is Linda artglass104. This is great information and everybody should read this as it valuable information as we test our glasses. You should always check the compatibility of the glass prior starting any hot or warm glass project. We deal with a lot of recycled art glass and we always recommend the following pull test:

The most common way to test coe compatibility is to take 2 small pieces (equal amounts) of the glass to be tested. Lampwork fuse both pieces together and stretch them - this is called a pull. If the glass pull stays straight the glass is compatible, if it bends like a fishing pole with a fish on it - it is not compatible. One glass is cooling faster than the other and this causes the bend.

One thing that hasn't been discussed in this is the possibility of chemical reaction. Even though sharing the same coe chemicals such as potassium (particles) has caused problems for our testing in the past. We asked at the studio where it was being batched why it was not sharing the same coe - the response was that it could be due to potassium. This can vary from batch to batch meaning that this could vary from one manufactor to manufactor as stated above in the postings. As more and more companies continue along the lines of Speciality Glasses I think that chemical incompatibility may become more of a problem as there are no standards and they try to out do each other. This was something that we were unaware of up until about 7 years ago when we were asking the same questions.

Glass is a continous learning process and it is great to have these kinds of forums to share information.

[JetAge Studio]

Linda, that's a very good point you made. I imagine there are many sources for the chemicals that make up these specialty glasses, sources available all around the world. Makes sense that these chemicals and minerals can have different characteristics just from where they were mined.
Kinda like wine; bad soil, bad grapes=bad wine, good soil, good grapes=a good time!
Renee

[artglass104]

Since posting to this I've talked with some of the locals here and they agree that chemical imbalance or difference could very well be a factor in problems they have had with supposedly compatible glass. They said that they have never taken this into consideration but consider that it may be a valid factor.

[glassbead]

Oh my goodness, yet another factor. It makes sense that the companies trying to "outdo" each other might cause some new wrenches to be thrown into the works. And of course, you can't always tell right away if something is compatible or not- it can take a long time for the stress to actually crack or break a piece. The folks who don't have kilns probably have a better feel for it that those of us who do. At least in my experience, the beads that are cooled in vermiculite often crack if there is any stress. Maybe I need to go back to the freezing and dropping method of bead testing- just to be on the safe side. And I doubt that any of us have the time (or inclination) to test each and every glass that comes our way. We just assume that the companies are already doing that.
My avatar bead found a home today- I'll miss that guy.
Again, thanks to all of you for your help.

[JetAge Studio]

Fortunately for those who DO have kilns, they can rule out a couple of factors that contribute to breakage.

The goal is to keep very good work "practices", that is, know your kiln (cant stress that one enough!), know your glass (as best you can), and repeat what is sucessful for you. Then, understand what glass "needs" in order to be used as a sucessful medium for you, the artist.
No, you don't have to be a scientist to understand glass. You can judge glass stress with various methods. You can do this with EVERY new glass you get (albiet, yes it's time consuming), so long as you have a "known" COE master glass to test with, and this is usually clear in the line of glass. Everyone can do it, and those with kilns have MORE tests they can perform! Most of the time you just rely on the manufactuer, but it is nice to know there is something you can do to test the suspect glasses.

When you know what to expect from glass because you treat it the same everytime (meaning; ramping temps, annealing temps, cooling cycle, etc), you expect a certain outcome. When you don't get what you expect (meaning breakage, or color reactions etc.) with multiple attempts, the glass itself can become suspect.

Not sure about your method of freezing and dropping the glass; glass remains stable at room temp if the stresses are relieved. Probably ANYTHING set to a freezing temp and dropped is suceptable to higher breakage, but then, I dont know. If you know your annealing schedule is correct, this type of test shouldn't be necessary.

Interesting stuff......glass!!
Renee

[glassbead]

The known COE master is a good idea. I never thought about just testing everything against one particular glass. That would make things alot easier.
As far as freezing- I didn't lose alot that way, but since I sell outdoors, there are times that my glass is subjected to freezing temperatures (though I usually try and avoid those days). Every once in a while, on a particulary cold day, something would just be broken. I attributed it partially to the temperature, so I just went ahead and exposed it so there wouldn't be any unpleasant surprises for my customers, or embarrassing situations for me. It seemed to work.

Laurie

[prairieson]

A couple more things to ponder...

COE isn't constant. As you heat and work the glass, the COE changes. The hotter and/or longer you work it, the more it changes. Its possible to create a base bead, work it hot and long enough, then encase it with glass from the same rod and lo and behold you've got incompatibility issues.

While the pull test is a good start it can also be misleading. An arrow-straight test result can, on occasion, be obtained with incompatible glasses. And conversely, a test result that's appears totally unacceptable can be obtained from two compatible glasses.

Go figure.

[Emiko]

The annealing temperature needs to be high enough to relieve the stresses that are present in the glass right after working it; I don't think 950 is high enough.

Glass anneals at the strain point or anywhere higher before it starts to soften, so theoretically Effetre can be annealed at 840 F. But there are reasons for the higher temperature range being recommended. Read either "Anneal Effetre at 870F?" here in the Tips Forum or "Mike Frantz: long overdue question" in the Kiosk. I got a very good piece of information from Craig regarding annealing temperature and posted there. (You don't have to read both.)

Basiccaly, you can't say that someone is annealing at too high or too low a temperature unless the pieces keep coming out of the kiln deformed, stuck or cracked because everyone's pyrometer and kiln work differently. Ryan says that he holds his kiln at 1200 F when he needs to pick up something to reintroduce it in the flame (in a different thread) and anneals at 1100 F. That's too high for most people and they would have flatening or sticking problem at such high temperatures. But those temperatures work for him because his kiln leaks heat around door, (and the pyrometer may be reading the tempreture higher than it really is.)

Sorry, this is a little off topic since the thread is about viscosity, not annealing, but I had to butt in when I read that remark.

[redsunset]

Thanks to everyone for all this great information. I had to come out of "lurkdom" to make a few comments. I have recently been making bigger, encased beads and thought I was annealing them long enough, but I was having, what I thought, was too much cracking. I've been madly gathering technical information from Jim Kervin's and Bandu Dunham's books and all the forums about COE and stress points, etc. It's really mind boggling how it all boils down to the science of how those molecules get along with one another and how interesting that COE might change, the longer or hotter, a glass is worked. This just goes to show that we can't create the art by color and design alone without understanding, at least some, of this information as we start to grow or change in our bead making techniques.

All I can say is, thanks, I needed that!

[JetAge Studio]

RedSunset,
You're absolutly right! There is soooo much to learn about glass's behaviours, and fortunatley, there has been lots of documentation over the years about this ancient material. My University (UA) has a whole section on the science of glass.....hopefully you have one too!
The most amazing thing about glass is that because of it's structure, it has the potential to have an INFINITE amount of recipes and formulations! I cant wait to see what's coming up in the future for lampworkers!!

Thanks for coming out of hiding and commenting!

Renee
JetAge Studio

[redsunset]

Having a science background made me fall in love with glass. I went to the 2004 Gathering by accident(?), and had never even heard of a glass bead. I asked many questions and when someone told me that when glass melts you are moving molecules around, wow, I was blown away! (Needless to say, I was making my list for my glass studio at the Vendor tables!) Now, as I'm learning the artistic side of glass and trying to develop the right side of my brain the understanding of the process has made me really appreciate some of the great glass artists that are out there and the techniques they have developed. These forums are a wealth of generosity by many of those people who love this art. This thread is one more example of the technical difficulties in working with glass, not to be dwelled upon, but at least thought about. Thanks for the nudge.
Kathy

[pearsonglass]

You also can think of it this way.

104 Coe is how much it will expand,, not when.

So you can have a glass that is COE104 and expands over the 850-875 range. You can have another 104 glass that will expand between 900 and 925.

They both expand and contract at the same amount, but not at the same temperature. There is no way to anneal these so they wont have stress.

These temperatures are pulled out of the air but hopefully you can see what I mean.

Brad Pearson

[prairieson]

Actually, by definition, COE tells you exactly when the expansion takes place.

If properly stated, COE is, in fact, the coefficient of linear expansion at a particular temperature range, the average expansion rate from room temperature to 572ºF (300ºC).

What standard COE ratings don't adress is what happens between there (300ºC) and the annealing and softening range. 104 glass does not have a COE of 104 in the 300º-500º range, it's something else.

[glassbead]

Oh my, what a can of worms. But lots of good information. I have to admit I don't understand enough of the scientific talk. I have, however, thanks to the info about Lauscha and the higher annealing temps mentioned here, started annealing at a higher temp. My kiln also leaks and has the pyrometer at the top, so it was probably not as hot as I thought it was to begin with. It is really too hot to play much here right now (only to reach 102 today), and I don't believe in air conditioning my studio, but I did make a large-ish fish yesterday with Lauscha clear, rubino oro and silver foil. So far it's alive, and this is often a recipe for disaster for me. I figured a little extra heating wouldn't hurt either, just to get all the stuff used to each other- I'm sure that makes no sense, but it made me feel better. There's nothing I hate worse than pouring sweat for 25 minutes, just to make a beautiful broken bead!
I know there are a lot of people who, when fusing, anneal over a wider range of temperatures, just in case there is a small COE difference. By starting my annealing process a little higher and slow cooling to 800, I should cover more of a range, right?
And yes, this started out about viscosity and COE, but it's all important and all related. The only way to make it all work is to connect all the dots!
Thanks to all of you.
Laurie

[glass-diary]

Hi glassbead,
Lauscha, Moretti, Vetrofond and ASK 104 (from Germany, KUGLER COLORS) has a Coe of 104 +/- 2 I guess. It is right: if the annealing temperature is high enough, the stress will be released. But if there are differences between different Coes, THIS problem can don`t be solved with this tip. 10% of the surface of the bead is the maximum for covering with a not exact right compatible Coe.
Good luck!

[glassbead]

I know this is a very old thread. But I was just regifted with some old formula Lauscha a couple of months ago, and I needed to read through this to be sure I remembered how to use it. And I was so amazed by all the info here, that I decided I should comment and bring this back up to the top again. Just in case anyone else needs help with these issues!

[Elizabeth Beads]

Interestingly, I just wound up with some 10-year old Lauscha (I think). So this is very timely information to have. Unfortunately, I use a lot of silver glass and anneal at a lower temperature for a longer time, so my old Lauscha may have to go to a new home.

[Conrad Hoffman]

This is a super interesting thread. I know a fair amount about COE in other fields, but near zero when it comes to glass. Glass and ceramics have tremendous strength in compression, but not so much in tension. It seems like a small amount of expansion internally would crack an outer layer. First question- does anybody find that layering one thing on top of another is a recipe for disaster, whereas changing the order works ok? Second question on annealing in general- how did they do it a thousand years ago? Did artisans have a feel for glass that was possibly better than we do today (lack of computers to waste time with ), or did they just put up with a lot of breakage? Pyrometer technology was probably not too advanced back then.

CH

[houptdavid]

"It would be better if we in the glass community had never
focused so much attention on the coefficient of expansion. We
need to stop talking about it as if it defines compatibility. The
only measure of compatibility is testing a sample appropriate
for the type of forming—whether blowing, fusing, pâte de
verre—and measuring the results. Unfortunately books and
manufacturers and teachers continue to print misguided
concepts and information. So—please—let’s quit talking about
COE and talk about the real issue: all the factors that contribute
to compatibility between glasses and how we can understand
and control them."

http://www.bullseyeglass.com/pdf/tec...chNotes_03.pdf

[LAJ]

I know this is an old thread, but am wondering if anyone knows of a list somewhere that has the different viscosities of 104 glass?

[Lisi]

It sure is an issue. Who would have thought all of these colors used together would be incompatible? Oh yes they are all 104, but they are not going to work together!

Effetre light sky blue
Effetre opal yellow
Effetre copper green
Efftre purple 254 (EDP)

Pretty combination, but one or more in the group does not want to play nice. Result: crazed crack city. Don't even attempt to try them together, it's a waste of time and glass.

Just an example on how you really can't trust any COE unless it has been factory tested compatible. Like Bullseye and Uroboros are.

[Firebrand Beads]

You can learn a fair amount from the pull-test, however. I recommend it before trying a new combination.

As for the question about order and layering, it appears to me that you need to have the stiffer glass on the outside, and the softer on the inside. For example, you can use 96 frits (sparingly) on the surface of 104, but not the other way around. This is borne out in paperweights, too - Loren Stump uses 104 for his flowers, etc. then uses a lower coe for the crystal encasement. I know that this also has to do with surface tension...

So - to tie back to the first part, if you have a curved pull test, but they are not too bad, you can generally get away with putting the glass that is on the outside of curve onto the outside of your bead. The one on the inside of the curve expanded and contracted more.