I've been thinking about glass--glassblowers in particular who are just about the coolest, hot people on earth. (I'll save my arguments here...)
Anyway, I'm wondering about what makes the red glass red--I think it's gold; and what makes the cobalt blue glass blue--have no idea; and then there's that green glass--is that just plain ol' sand, ash, and the other third thing I can never remember that causes natural green glass? And how about clear glass? What is it called?
If anyone knows what these colors of glass are properly called, I sure would be appreciative of your posting that info here. And if you know what makes 'em what they are in the blowing, even better! And, if you've never personally seen a glassblower at his/her work, well, you just ain't lived yet!
From the other side of the looking glass,
WindWrought A vessel produced by a glassblower's oh-so-skillful mouth
Cobalt is the metalic element they use to make the glass blue - thus Cobalt blue (which, is a colour I absolutely adore).
I don't know about the other colours, though I'll be very interested in finding out.
"Probably the second most asked question is....."How do you make different colors
?". That can be done by adding the precise amounts and combinations of various metal oxides. With Cobalt Oxide you get blue, with Iron you can get green, with Gold you can create a beautiful cranberry colored glass.(and a rather deep hole in your wallet) The coloring agents we will be using for our Ruby are Cadmium and Selenium. "
How colored glass is made:
http://www.ironandglass.com/howglass.htm
Dear wwh,
I knew you'd come through with a link--just knew it! Thanks a lot. It would be good to see the elements/minerals/whatever used to get all the different colors of glass.
Best regards,
WordWindowpane
Dubya, glad you brought it up, i love glass. any one passing through NY State on their way to wordapalooza might want to stop at Corning, and visit the glass musuem.
CK and SWMBO passed on it (as i recall, he said something to the effect of $10 a piece was a bit too much to pay to see some glassware?!)
but i love it. they have giant (three footers or so) glass springs-- that they compress about 10%!, and then they spring back! an a column of glass, 10 feet long (3 + meters) that is so clear, you can read a newspaper (you stand at one end, the newspaper is 10 feet away!)
they have ancient glass-- imagine, a small glass bottle, 5 thousand years old, and still intact! (this coming from a person who has to replace her drinking glasses ever 5 years or so!)
they have the stuebens glass factory there too, you can watch the glass blowers go into the the honey pot of molten glass and lead, and before your eyes, form a crystal sculpture!
(CK, you were wrong to miss it, IMHO!)
Thanks for the site Bill. It will take some time getting through it all but it is really interesting so I marked it off for after my AWADing.
=======================================================
Corning sound like a good idea Helen. I wonder if it's open year-round?
I wonder if it's open year-round?
Yes, it is! And it is a beautiful place to boot! Corning is easy to get to, and the factory has an admission price under $10. We have been there many times and it always fascinates me. I watched a glass worker with a solid rod of glass create a teddy bear. After the demonstration, and after a cooling period, my husband purchased that same teddy bear for a small fee. It is something I will always treasure as a gift from him on our honeymoon.
In pottery glazes, minerals are the basis for the glazes as well. They are mixed, or not, and made liquid for dipping or application with a brush. There are many recipes for colors of all kinds. Dangerous metals are no longer used in glazing pottery (i.e. lead) but raku, a very shiny, showy type of glaze is not reccomended for dinnerware or coffee mugs. Some glazes are still somewhat dangerous to potters if care is not taken in the application, but are safe when fired. It is not reccomended that pregnant women glaze pottery. A glaze is a "glassing" of the exterior of the pottery. But, y'all knew that.
All you sci-fi fan-- help me if you can-- there is a wonderful story about a Yellow glazed bowl..does anyone remember who wrote it? or the name of it. (it might be the The Yellow Bowl)
and there is some beautiful yellow glass in the Corning museum, and both the glaze (in the story) and the glass, in the museume, are created by the addition of uranium salts! the corning museum has a geyger counter near the glass (or it did year ago) the glass has a very low level of radiation, and needless to say, its not recommended for use, but oh, what a yellow!
Dear of troy: perhaps you are thinking of Ming Yellow. There was a story about it in Saturday Evening Post almost sixty years ago.
Dear wwh,
This story, "Ming Yellow," was the the Saturday Evening Post sixties years ago and you still remember it? It must have been one sockeroo of a story!
Best regards,
WememberedWords
Dear WW: I still regret the passing of the Saturday Evening Post. Every week there were four or more fabulous short stories, of which I remember part of plot. Also marvelous serials. I wish Yahoo had them archived.
A natural pheonomenon of the making of glass is that of lightning's fulgurites. Flash of lightning! Directly into the desert sand! And the result may be the rooty network of glass called the fulgurite. Wow! No ash, no bone--just flash of lightning and sand. Wonder whether Corning could duplicate that effort and patent it?
Off to see my Sky King,
Orb~
A long time ago I read about about the Soviet spy Kim Philby's father seeing large meteorite hit in sand in Arabian desert, making large area of melted glass. Can't find anythi;ng about it on Internet.
When I took a radiation protection class as part of my Master's degree, the prof brought in an orange dish glazed with uranium as an ingredient in the colour. Again, what a great colour! (The pedagogic purpose was to try out different types of radiation detectors to determine what type of radiation was being emitted by the plate - since it was alpha radiation it doesn't even go through your skin, so it wasn't exactly dangerous for us in class It's only dangerous when it's inside your lungs or gut!) In the same lesson we checked out the radiation from a radium dial watch, and two different types of smoke detectors - one commercial, one for home use. It was a really neat class.
I just started reading a wonderful new book by Oliver Sachs (author of Awakenings and The Man Who Mistook His Wife for A Hat) called Uncle Tungsten. It's a memoir, and in his childhood he was keenly interested in chemistry, particularly the colors of various elements and alloys and the colors made when they reacted with each other -- fascinating stuff!
Corning glass museum was US$11 to get in, and our budget wasn't up to it by then. It wasn't meant to be (that) derogatory a remark!
Has anyone ever seen a fulgurite?
Just wondering....
Lover of meterorites and lots of things that end in "ite,"
OrBite~
As a matter of fact, my friend with the jewelry store has a pendant made out of fulgurite. It's an odd shade of green and wriggles. (well, it does if you squint your eyes just right!)
i don't think i ever have (seen fulurite) but i love obsidien, natural glass.. my favorite is snow flake obsidian
i think obsidian is formed by volcanos-- certainly, it is almost always black.
[smug -e] I have a fulgurite - found it in a sand dune during a First Year geology excursion at Long Reef, one of Sydney's northern beaches.
It isn't glassy, the exterior being quite granular. The grains lining the tube seem welded together.
I originally thought that it may be a fossil crab burrow, but numerous people have since concurred that it's a fulgurite.
stales
Tektites are another form of naturally occuring glass.
The consensus these days is that they are cooled droplets of the earth's crust flung up during an asteroid impact - or during large volcanic events.
Thailand is well known for dark green / black tektites; in Australia we have black (smoky when polished) ones (called Australites - got a nice one of these from Kalgoorlie); but the prettiest of all are Moldovites - champagne bottle green and often intricately etched.
Just to throw in a word link - there's a whole terminology associated with tektites. Things such as buttons, flanged buttons, teardrops, partial flanges, dumbells - let alone the various types of tektites. Have a squiz at the URL given...
Good URL at
http://www.crystal-world.com/html%20pages/meteorite%20pages/tektites/glassy_tektite.htm It mentions several other types as well.
BTW - all glass is, in geological terms, quite unstable. Glassy rocks and tektites relatively rapidly break down to clay.
stales
In reply to:
i think obsidian is formed by volcanos-- certainly, it is almost always black.
Obsidian is black? One of my favourite exhibits at the Museum of Mankind in London (I have this vague idea the museum is not there any more, having been reabsorbed into the British Museum) was a "glass" Aztec skull. I'm sure it was described as being made of obsidian but was the normal transparent non-colour of ordinary glass. It really was beautifully carved and a fascinting object.
Bingley
Ackshully®
cheque is in the mail, Mav, now that I see my options
Thanks, stales!, the pendant in question is really Moldovite. It is the color and wiggliness (champagne green and intricately etched) that you described. I couldn't remember what he called it, but I knew it was not of this world.
Ah, Stales, you should be smug! To have a creation of lightning in your hand! That's a great gift of nature, isn't it?
I just wish there were better names for fulgurite. Would love to know more names--even in other languages--for this lightning glass.
Best regards,
WW
I have read that glass is a super-cooled solution. When it is molten, the rate of cooling makes big differences in its properties. It has to be cooled very slowly.The huge panes used in modern buildings have to be tempered, or they would shatter too readily. The glass in automobile windshields is treated so that when it shatters, none of the pieces are bigger than a fingernail. The old windshields could make swords that could inflict gruesome wounds. When I was a boy testing urine specimens, the test-tubes were exasperatingly fragile. They had to be warmed up very slowly in the alcohol burner flame, or they would shatter and spill the urine. So, the invention of Pyrex glass was a very great blessing.Adding some borax made a very great improvement in both thermal and mechanical shock resistance.
And the first telescope lenses were very disappointing because of rim of color, called chromatic aberration. Many years went by before it was discovered that special optical glasses could greatly improve the quality of the image. That's why your camera lens is not just a single piece of glass, but three of four lenses of different composition nested together to avoid both spherical and chromatic aberration.
P.S. The big telescope mirrors take as much as six months to cool, to minimized internal stresses.
Thanks for the info wwh - concurs with what I've heard. Taking it further though, somebody once told me that the fragments of safety glass (basketball's "ice shower") had achieved solid status (from being a super cooled liquid).
Also heard that glass retains its fluidity throughout its "working" life. One of the characteristics of a fluid is the ability to flow - which is exactly what glass does. Apparently the glass in windows ever so slowly succumbs to gravity, to the point that the window panes in old churches (frinstance) are thicker at their base than at their top.
Just another couple of bits of trivia about the colouring of glass....
A friend of mine collects old (say 1st half of the 20th century) glassware. Things like cake plates and so on. He leaves them on top of his garage roof in the blazing Perth sun for a couple of years until they turn that beautiful amethyst colour I presume we've all seen. They look stunning. Obviously (help Bean!) it's the sun's gamma(?) radiation that sets off the trace elements in the glass. My friend cites it as being due to the presence of uranium in the glass - but obviously not to the level that produces the deep yellows mentioned earlier in this thread. He also told me that the inclusion of uranium in glass was banned in the 50's (unsure of the date).
Gamma radiation is used commercially to produce coloured quartz - presumably in a similar (but shorter) process than my friend's garage roof! Clear quartz is turned a whole range of yellows, lilac and so on through this process. Some of you may have seen the bi-coloured gem "ametrine" - half lilac, half yellow. Very pretty but, for me, being artificial, not that desirable.
In a similar fashion, the vast quantities of amethyst produced by Brazil and India are often heat treated (I believe they are simply baked in an oven) to produce butterscotch orange "citrine" or black "morion". Both are naturally occuring varieties of Quartz but, IMHO, buyers should be aware that they are acquiring an "enhanced" or "altered" product. (It'll never happen so I won't lose any sleep over it!!)
Finally, whilst I haven't seen (first hand) the reds and yellows discussed above, the mineral world has a couple of magnificent offerings - realgar and orpiment. These are closely related sulfides of arsenic with stunning depth of colour. They were used historically by icon artists, the crushed mineral being mixed with egg yolk to make the paint.
Well that turned out to be a bit of a mixed bag hey!
stales
Wow, what an astounding array of information on glass. I knew that glass was a very viscous liquid (at least most glass) and always wondered about how much activity really occurs in a pane over the years, so thanks for that info stales.
I don't really know too much about physical glass, but I was so intrigued, that I decided to look it up for yet further clarification:
'Any of a large class of materials with highly variable mechanical and optical properties that solidify from the molten state without crystallization, are typically made by silicates fusing with boric oxide, aluminum oxide, or phosphorus pentoxide, are generally hard, brittle, and transparent or translucent, and are considered to be supercooled liquids rather than true solids.' AHD
Aside:
Glass is also the name of a famous American minimalist, (Philip), who wrote a piece for 12 keyboards, and during the first performance thereof a lady started screaming and there was an awful ruckus the likes of which hadn't been seen since 'The Rite of Spring' debut.
Fulgurite pix - NOTE: Commercial site (not stales related but)
http://tektitesource.com/Fulgurites.htmlFTR, mine's like the top ones.
stales
Dear Stales,
Wow! Thanks for providing the link. I especially liked the $250 one that had been sold--not that I would ever buy a $250 fulgurite!--but liked it because it was more suggestive of lightning than the others and also because it reminded me of antlers, which are a constant passion of mine.
Anyway, thanks again!
DubDub
I knew that glass was a very viscous liquid (at least most glass) and always wondered about how much activity really occurs in a pane over the years,
It's not only old churches that have drippy windows. Even 18C houses show evidence of the viscosity of glass. To go off on a little glassy tangent, if you know that a building's window glass is original, it can be used to (roughly) date the house. The earliest form of window glass is called crown glass. It was blown out in a large flat circle, and then rectangular pieces were cut out of it. This leaves concentric arcs of bubbles and other imperfections in each piece. The small central piece of the crown, called the bullseye (with a little nub from where it was attached to the blow pipe) was often used in transoms or front doors. Around the turn of 19C (I think -- I don't have my reference books here) a process was developed to make so-called cylinder glass. A large sphere of glass was blown, and then that sphere (still attached to the pipe) was swung back and forth in a heated trench, so the sphere would stretch into a cylinder. While still slightly molten, the ends would be cut off and the cylinder was cut down its length and unrolled to form a flat rectangular piece that could be cut to size with much less wastage. Cylinder glass, therefore, has long, stretched-out bubbles and imperfections in parallel lines. Drawn glass was developed c.1915, in which the glass was simply pressed into sheets with asbestos rollers and finally float glass (in which the glass cools on a bed of molten tin) was introduced in the 1940s. Float glass is the most optically pure, but it has none of the character of the old handmade glass.[/tangent]
Oh, and welcome back BY!
RE: Float glass is the most optically pure,
Float glass is made by floating molten glass on large pans of liquid mercury. it float across the surface!
(clearly we have some glass fans here!)
The cradle of early American glassmaking was right here in South Jersey. The abundance of silicate sand, access to navigable waterways, and forests for wood led to a colonial glass industry here that boasted upwards of 225 glass factories well into the 19th century. One of the foremost of these was the Wheaton Glass Co. (my brother-in-law's name, but no direct relation to the glass moguls).
Today there is a restored historic village, Wheaton Village, in Millville, NJ, where you can watch and study the art of Early American glassmaking. And it also houses the Museum of American Glass, with over 6,500 pieces of vintage glass for your delicate perusal! Here are the URLs for the full story. The museum link also has photos of some beautiful pieces. The other link describes the village, it's purpose, and gives a capsule history of Colonial glassmaking (no wonder you Brits didn't want to give up New Jersey!
...like I always say,
"Get Off the Turnpike!"®)
:
http://www.wheatonvillage.org/museum/http://www.loc.gov/bicentennial/propage/NJ/nj_s_lautenberg1.html
floating molten glass on large pans of liquid mercury.
Helen, this is absolutely fascinating. Thank you!
Looking around, I found that sometimes a bed of molten tin is used. Does anyone know when did this "floating" process came into vogue, and why it was not practical earlier?
Stained glass windows in churches often suffer, after some years in a warm climate, from sagging as a result of the stretching of the lead framework into which the glass is set. This happened in our church. They had to be taken down and somehow ironed out to get them back into their original configuration. We were lucky none of the pieces of glass fell out.
On Beacon Hill in Boston there are some very old houses and some of the window panes, original to the house, have turned a delicate lilac from sun .... and owners are very proud of them. They go to great pains (groan) to protect and care for them.
There is an old saying about glass and its fluidity when heated and its fusion as it cools :
"Any idiot can tie knots in glass but it takes a Master to untie them."
(neatly bringing thread back to the skill of glassblowers) {smug grin -e}
'Er indoors and I went to a glassblowing place in a village above Monaco called Éze last week while we were staying in Menton. The blowers were working right beside the retail counter and were very casual. But skilful with it.
I used to work for a glassblower. He was amazing. He also had a keen business sense. He said people buy 10x more if they see you blowing anything glass.
Bob, they 'ironed' lead? Did that make it stronger?
Wow, sometimes your puns are panefully transparent...
And yes, definitely good to see you again, Ladymoon! I'm sure your former boss was right about customers buying more when they see glass blown. It looks magical. Dick Francis' last book had a glassblower as the main character. This book, like all of his, has some informational material on whatever the character's trade is.
Check your Email, Jackie!
Many years ago there was a glass factory in Sandwich, MA, near east end of Cape Cod Canal. They made very attractive cut glass formal table ware. My mother had a very fragile glass cabinet of pitchers and goblets. Many scoldings I got for running through the dining room, because the vibrations might damage one of the goblets. They were just for looks. I don't remember their ever being used.
My son does not believe me about this whole glass being a super cooled liquid thing. Does anybody have a web site they can refer me to so that I can say "et vlan."
a more common liquid, that has some of glasses properties, is silly putty!
it is more liquid, but if you give it a sharp snap, it pops, and breaks "clean". think about? does liquid water ever snap and break clean? no! there are lots of others liquids that behave "unliquid-y"!
trouble is, your son thinks all liquids follow the "general rules" for liquids..(ie the rules first noted by Newton, i.e., liquids flow, (they don't hold there shape) they take the shape of what ever contains them, there viscosity is effected by tempature (actually this is true of glass at high heat, but not at "room temperature", and so on.)
for example... think what would happen if you put an electric mixer (turned on!)into a full bowl of water-- a shower! (a common liquid, acting as we (and Newton!) expect.
but take an other liquid (here you have a choice-- egg whites, or STP motor oil treatment!) turn the mixer on, put them in the bowl.. and no shower.. in fact, rather than being flung away (as water and most liquids would be) egg white and STP cling to the beaters! (that why STP works in your engine, the actions of the engine actualy attract the STP, and increase the lubrication effect!)
Glass is not a common liquid, and it doesn't obey the general rules. but "non-newtonian" fluids are fairly common.. send me a PM for more interesting "kitchen science" experiments!
Dear belMarduk: I searched Yahoo for "Physics glass supercooled solution" and got this URL. It is very hard reading, but at least your son can gather that the idea is scientifically accepted.:
http://www.ttu.edu/~chem/faculty/quitevis/quitevis.html
Dear belMarduk: if your son likes to do simple experiments, here is one about glass he might enjoy. Prince Rupert (let your son look him up) was a scientific dilettante, and is credited with discovering that if a glass rod is melted in a burner flame, and allowed to cause drops of molten glass to fall into the water, the resulting "tadpoles" have the peculiar property of breaking into tiny pieces if the tail is broken.
http://www.thecure.com/robertpages/princerupertsdrops.html
Yeah, the cause is similar to "silly putty" it has to do with how the molocules are aligned, especially under stress.
Under stress, silly putty's molocules align at right angles to the stress, so a sharp pull, results in a clean, almost sliced surface.. (where as gentle pressure cause it to stretch.)
dropping hot liquid glass into water, causes a sharp cooling effect, which lines up stress in the glass..
depending on your utility service you might be able to do it over a kitchen stove..
Starting in the 1950's Con Ed added water vapor to the natural gas, so you get few BTU out of a given volume. (you used be be able to melt lead, for plumbing work over the stove!) now you need to use a butane torch.
an other cool liquid, is a suspention of corn starch.. add enough corn starch to about two cups of water (about 1 cup) to make a fluid about as thick as cream.
pour into a pie pan, or some other flat shallow dish.
Rapidly, and hard, smack the fluid! No, no splashes! it too, aligns its self under stress. and a hard smack causes the liquid to behave like a solid! leave your hand there for a moment or two, and you can feel it return to liquid state, and you hand will gentle sink in!
Quite a while ago, there was a thread that mentioned thixotropism. When penicillin was first used, it was in a watery solution. But then a creamy liquid concentrate was developed that looked as though it would not go through a fine needle. But it had the property of becoming much less viscous when drawn into a needle. This is called thixotropism. I don't know how it was achieved.
Why wasn't Science classes this much fun and interesting?
Great thread.
Thank you all.
I don't specifically about thixotropism but chemisty is interesting--the more i learn about structure, the more interested i am
carbon (wonderful stuff!) pure carbon can have its molocules aligned one way, and they are collapsed, flattened, and then slide over each other almost like grease(graphite)
aligned an other way at rigid angles and you have a crystal form-- diamonds!
We tend to see solid things as solid-- but on a molecular level, things are not the same..
a classic fun "magic trick" is to take an equal volume of water and alcohol.. (say one cup of each) Use a measuring cup! then pour both liquids into a 2 cup vessel-- You end up with just over 1.5 cups of liquid! (you do need a high proof alcohol, but it can be "denatured" tax free undrinkable stuff!)
Its an amasing trick! the alcohol molocules fit into the empty spaces in the water. Its hard to imagine a solid as dense as water has having empty space.. but it does!
thixotropism is a property of gels and emulsions to become liquid when aggitated or under stress. sort of the opposite of the corn starch water mixture.
A couple months ago there was a thread about mudslides from volcanoes and solifluction from earthquakes. Another source of homes being destroyed is "quick clay" which with only slightly greater than usual rain can cause a previously stable slope to collapse catastrophically.
A use of "liquid glass" a hundred years ago was to preserve eggs for baking. A surplus of eggs immersed in it could be used months later. I suppose it worked by excluding oxygen.
An extremely important form of carbon is what used to be called "activated charcoal". In organic chemstry it was invaluable for its power of removing small amounts of impurities from crude synthetic product.
Probably its biggest use it removing molasses color and taste from sugar. It can also be used to remove some pollutants from water. I don't know how the "activation" is achieved.
A use of "liquid glass" a hundred years ago was to preserve eggs for baking.
Good grief, Bill--how did they get the eggs out, do you know?
The liquid glass was just a syrupy solution of sodium silicate. It rinsed off readily. If I remember right it was called water glass.
PS from my dictionary, water glass, definition 4:
sodium silicate or, sometimes, potassium silicate, occurring as a stony powder, usually dissolved in water to form a colorless, syrupy liquid used as an adhesive, as a protective or waterproofing coat, as a preservative for eggs, etc.
I have never done this, but someone I know put liquid glass in the engine of his dying car so that it wouldn't be obvious to the unsuspecting buyer that the car had serious engine trouble. It worked. He sold his car.
Poor baby that bought it. You can still find liquid glass in some pharmacies.
of Troy--Thanks for the water/alcohol trick. Wonder which other liquids would give the same sort of results?
Consuelo--how did pouring liquid glass into the car's engine conceal its flaws?
How much heat to melt a window before your very eyes?
OrB~
OB- I'm not real sure, but I think it had a cracked engine block and the liquid glass sealed the crack. He changed the oil and the radiator fluid. I don't think it was a permanent fix, though.
You can melt glass with a butane burner.. the same kind you use to solder pipes. thats what glass crafters use at fairs, plain glass tubes, clear or colored, that the melt and form into little glass animals.
My microwave came with a double tiered rack, and when one of the insulating covers on the foot broke, my son melted some scrap glass and fashioned a new glass insulator in a week or two. (sometime i am amazed that my kids never blew up the house, or burned it down!)
as for the water/alcohol trick, yes, i am sure there are others.. i just don't know any off the top of my head. that one works well because both water and denatured alcohol are easy to buy and reasonable cheap.
there is an other, one, a simple salt (not table salt, but some other salt) that turn water pink/red, add something else, it goes clear, and other salt, and now the water is blue..
(i was made to do recertations as a child, and i made my kids do something come the holidays.. my son did magic tricks.. he got quite good at them.)
Dear of troy: is the material that turns from red to blue by any chance "litmus"? I did not know until I just looked it up that it is produced by a lichen. It turns pink in acid, and blue in alkali. Sometimes "litmus test" is used as a figure of speech meaning a simple test for a desired condition. It used to come on little strips of paper, and was very easy to use.
Ooo, I remember those little pieces of paper. Dipping them in test tubes to see if something was acid or alkaline. I have heard the "as a sort of litmus test" expression, but very seldom. People usually say "let's see if it pans out."
I'm guessing, but I reckon a cup of sugar, or a cup of salt (and many other soluble things) would produce less than two cups of fluid once added to a cup of water.
Mind you, I don't know if you can dissolve one cup of sugar in one cup of water - it may not go......
stales
Dear Stales,
Just heat up that sugar in water, stir it slowly, and you'll at least get somethin' you can pour over your engine when you want to sell your broken down car. of Troy taught me that trick!
Best regards,
DubDub
Regarding Helen's cornstarch trick - If you take that concoction in your hand, and squeeze it, it feels solid, but then let your hand relax, and it runs out of your hand. Quite something! I used to do demonstrations for elementary school classes about chemistry, and that was always a fun one. They call it "Magic Mud" up here. There's a kids' magazine about science called OWL Magazine, and in it, Dr. Zed (not Zee!) has an experiment every month. One of his most famous is the Magic Mud.
Hi Helen,
sometime i am amazed that my kids never blew up the house, or burned it down!
when I was a youngster, my parents must have had similar apprehensions about my "laboratory" in the basement, e.g. when I heated sulfuric acid, and the vapors floated up the stairs. I also made glass on a little home-made furnace where a blower pushed burning coals up to 1500 degrees centigrade. Ruby glass uses a tiny amount of gold chloride, so it is not especially expensive from that point of view, but the color only develops on tempering the glass when it has first cooled down, and that's where secret art comes in.
There was a story about it in the Saturday Evening Post almost sixty years ago.
I must've missed that one, wwh.
Here's a description of uranium glass from the Museum link I provided above (actually a link on the link). If you click on the url below you'll see a great picture of uranium glass, and when you drag your cursor over the pic you get the florescent view.
Yellowish-green
transparent glasses are
known as vaseline, canary
or uranium. Popular for
pressed glass novelties
and tableware during the
1880s and 1890s, this
glass utilized uranium
oxide as its colorant.
When subjected to
ultraviolet (black light), it
fluoresces lime green. Clicke here for photo:
http://www.wheatonvillage.org/museum/uranium_glass.html