How your glass is made

[pam]

Hi all, I just found this article I wrote a while back and thought some of you might enjoy reading it.

How Glass is Made

Many of us flameworkers may have entered into the art glass field having never been involved with glass. We all grow up with a familiarity with glass, from drinking glasses to the lenses we wear to give us clarity of vision, but what do we know about how glass is made and what to look for when buying glass for your art?
The common glasses we see in items such as drinking glasses and even window glass are generally made from three primary materials, a former, a flux and a stabilizer. The Former is the basic ingredient and the most common former is white sand, silica, which has a melting temperature of 3360 degrees Fahrenheit. The Fluxes help the Formers melt at a lower temperature. Soda Ash is one such Flux. Fluxes, however, also make the glass chemically unstable and thus a Stabilizer is added, such as limestone. With these three basic ingredients we now have the makings of soda-lime glass. Different additives in small amounts are also used to improve the quality of the glass. Every glassmaker has his own secret formula.
The dry ingredients are then blended together prior to placing them into a furnace to form glass. The blended ingredients are called batch. Placing the ingredients into the furnace is called Charging and it’s generally done in small increments, starting with, for instance, 15 pounds of batch, and after an hour or two, once that batch is melted, adding 25 pounds, waiting until that is melted and continuing to add in 25-pound increments until the furnace is fully charged. A furnace may hold 150 pounds of glass. After the last charge the temperature in the furnace is raised to about 2450 degrees. The batch must be held at that temperature for around eight hours to fully melt.
To check the progress of the melt, you can take small gathers and look at the bubbles. At first you see millions of tiny bubbles, then later you see fewer, larger bubbles. When the bubbles are all larger than pinheads, you turn the temperature down to your working temperature, or just below, to squeeze the bubbles out, a process called Fining. This will take another eight hours. The bubbles found in the glass are byproducts of the melt process, generally C02. This high temperature and this amount of time are necessary because glass is a viscous material and it takes a long time to rid the glass of the small bubbles. They must be removed to make the glass structurally sound, stable and durable. Once the glass is bubble-free your melt is done and you are able to use the glass.

When buying glass, look for glass that is free of bubbles, called seeds, and free of stones, which are ingredients that were not properly blended during the melt.

[Tancaro]

Interesting Pam. Thanks. I had looked for this type of information many times and just couldn't seem to find it on the internet anywhere. Was your article published?

-C

[pam]

Thanks. Glad you enjoyed it. No, I don't think it was ever published, although I'm not certain. It was actually written for a presentation.

You can find lots of info on the CMOG website, along with a few others and in Glass Notes
by Henry Halim. I used to blow glass and remember fondly the wonderful nights of charging the furnace and testing the glass.

[Hayley]

Thank you, Pam! I have read about glass making but it's never be presented in such an easy-to-understand way!

[MaryBeth]

That was truly interesting! Thanks:kiss:

[stargirl]

Thanks for the info Pam...I have always wondered how the glass that we use was made.

[nagibeads]

thank you so much Pam--you are a wonderful wealth of knowledge!!

[volkanokaren]

Neat!!!!

Karen
Volkano Exotik

[Mama Teesa]

Thank you for posting this!

[lunamoonshadow]

So cool! Thanks Pam!
(and...I'm showing this to my mom, 'cause she's an information junkie too :D)
I'm surprised you never sent it to someplace like the Flow--there's lots of folks who'd like the "basics in easy to explain language"--if not for themselves, as an example of "how to explain it to their customers without watching their brains fall out of their heads" ;)

[pam]

Thanks again, everyone. I guess when I started making beads everyone sort of knew things like this already, because they had "grown up," so to speak, in glass. Imported lampworking rod had yet to become generally available and you had to know more about the glass you were buying than the colors to be able to make glass beads.

Move forward twenty years and what we have available to us as beadmakers in the US and around the world, thanks to Pat and Mike Frantz and Bullseye and a couple of other good companies, is a wide array of first quality glass. When people buy Effetre or Bullseye they know they are getting good glass, therefore many people have never experienced bad quality glass. I bet the Effetre factory does not even know how to make bad quality glass and wouldn't even let it out the factory doors. The same can be said for Bullseye. Their quality control is extremely important to them.

There is a real art to making glass and no shortcuts or the result is just bad glass. Glass that is not made properly can weep, erode and crumble over time, or even dissolve in water (or so I have heard). I think I have seen seconds on sale at times of Effetre, but they are called just that, seconds, because the quality is not up to the standards, and none of that is unfined glass. There is a real art to making glass and no shortcuts or the result is just bad glass.

I read a description once that really stuck with me about making glass. It compared making bread to making glass. When you make a yeast bread you have to let it sit and rise, bubbles form and the bread rises. If you don't give the bread the time to rise, you have a leaden viscous mess. If you put properly made bread in the oven, but you are in a rush to bake it, so you increase the temp to high and bake it for a much shorter period of time, what you get is a loaf of bread that is burnt on the outside and still raw inside. It kind of equates to glass, if you don't follow the recipe and try to take shortcuts to save time you end up with a gooey mess.

[LoriBird]

I've seen how they make glass on the show "How It's Made". They were making window glass. I love that show.
Of course my kids hate it...they say it's boring. Yanno, they might learn sumfin. :poke:

[Drafly]

Hi Pam, That is a great article and the anology on the last post is "right on." If anyone is ever in Spruce Pine, North Carolina, they make batch there. They have great buys on frit, as they carry almost every colorant there is for their batch. They also stock about every size in frit.
Jim Clark

[Troll Lover]

Thanks Pam, that was fun to read!

[klcbeads]

Thanks for the info Pam!

[Gila]

Thanks Pam, mind if I save a copy?

[pam]

Of course you can save a copy.

[Hayley]

woohoo I save one too! Thank you so much, Pam!

[pam]

You're very welcome, Hayley.

[Gila]

Thanks Pam!
How about sharing it with others, if the source is credited?

[lunamoonshadow]

Hi Pam, That is a great article and the anology on the last post is "right on." If anyone is ever in Spruce Pine, North Carolina, they make batch there. They have great buys on frit, as they carry almost every colorant there is for their batch. They also stock about every size in frit.
Jim Clark

That would be a bad, bad, bad place for me to visit....prolly even worse if Nikki & I went together :lol: (we'd need a U-Haul!)

[pam]

You actually would need a u-haul. The place is great, visited there many times while taking classes at Penland. I love the place!

[Listenup]

Thanks Pam. I appreciate this info.

[Drafly]

Pam, Don't you love Penland? The food is great too, if you like country cooking. I used to sell Penland pottery supplies and deliver them. Did you meet Cynthia Bringle?
Jim

[pam]

I do love Penland, just the atmophere of all these artists in one place is insprational. Yes, I went to Cynthia's studio and actually bought one of her pieces.

However, I have to disagree with you about the food, and I do love country cooking, but what we had was not country!

[Drafly]

You are so correct about that place. It has been thirty years, since I was there. At that time, they used mostly local produce from farmers in the area.
We had ham buscuits, fresh corn on the cob, brown beans, green beans, okra, cornbread and strawberry shortcake. They used a dolly to wheel me out.
I loved Cynthia's work. I bought some and traded her supplies for some. I have about thirty pieces of her work. I loved her goblets, all one of a kind. She used to visit us and would jump on me for not using them for every day.
Pleasant memories.
Later, Jim

[FishBulb]

Thank you for this information Pam! I had always wondered about this.

[Hels]

Hiya:). Great article Pam!!

Here's another one I saved from the net a while ago from the Museum of Glass:
http://www.museumofglass.org/education/learn-about-glass/science-and-glass/

Gives a recipe for making Soda Lime Glass as compared to a Chocolate Chip Cookie recipe:
Soda-lime Glass Recipe
72.0% Silica sand SiO2
14.9% Soda Na2O
7.9% Lime CaO
1.8% Alumina Al2O3
1.0% Lithium Li2O
1.0% Zinc Oxide ZnO
0.5% Barium BaO
0.4% Potassia K2O
0.2% Antimony Sb2O3

Plus Flux, Trace, Fining Agents, Decolorants. Here's the Trace for example:

The Trace Ingredients

These are the "walk softly, but carry a big stick" constituents. Small additions of other chemicals are included in the batch to sweeten it, balance it and give it some complexity. These "intermediates" are not capable of forming glass alone; rather they assist in strengthening the glass and increasing the working time.

Alumina (Al2 O3) is added in small amounts (1-3%) to increase the chemical durability of the glass.

Feldspar (KNaO Al2O3 SiO2) is another compound that can impart alumina into the melt, with additional silica and potassium hitching a ride.

Lithium (Li2O)is also a powerful flux. It is added to soften the glass, decrease its viscosity, and lower its melting temperature.

Barium oxide (BaCO3) lowers the melting temperature, decreases the tendency towards devitrification (the formation of crystals within a glass) and offers a higher refractive index. It is also toxic.

Zinc oxide (ZnO) is added to increase the brilliance of the glass. It works well with colors, extends the working time and also reduces devitrification.

The article lists all the coloring agents as well, which is really neat.

This is my favorite of the info articles, but there's quite a few more with specific recipes, ingredient details and info too if anyone wants more data. I thought I was the only person crazy enough to care about this stuff:).

[BeadMaven]

Thanks for the info Pam, I too had always wondered about how glass it made.

Nice addition Hels...now if they could just add a teeny bit more barium oxide to the EDP and Mocha I'd be tickled. :lol: