Re: How can we make glass at home?

Glass is very interesting stuff, but it probably isn't a good idea to try to 
make it at home unless you're interested in spending a lot of money for 
melting, homogenizing, and annealing furnaces -- as well as buying some pretty 
exotic tools for blowing or forming it.  I’ll suggest some easier and cheaper 
ways to get your magic trick going toward the end of my answer.

First of all, let's go through what glass is and how it's made.  Generally, 
glass is composed of the oxides of several metals that are melted together to 
produce desirable properties.  Some glasses have ten or more different oxides 
in their composition, but a lot of the more common ones have oxides or 
carbonates of boron, sodium, calcium, lithium, aluminum, lead, silicon, and 
potassium in them.  One of the most interesting thing about glasses is that one 
of the materials usually melts at a lower temperature than the others and then 
proceeds to dissolve the other materials at temperatures well below where they 
would melt themselves individually.  While this may seem strange for things 
like silicon dioxide (which is just sand!), it's not really so odd when you 
think about how salt readily dissolves in water at room temperature -- but only 
melts at a temperature of many hundreds of degrees C.

In any case, after all the desired oxides are dissolved into one another the 
molten mass is generally stirred as it cooks.  Often, one or more of the 
constituents reacts chemically with one or more of the others in a complex way 
-- sometimes giving off gases and sometimes just changing the chemical bonding 
state of the atoms involved.  Because glass forming temperatures are usually 
very high (above 500 C is common), you need special furnaces to melt the 
constituents and you also have to stir them – sometimes with iron paddles, 
sometimes with exotic materials like platinum if the glass constituents are 
aggressive in attacking iron.  After the glass has been melted or cooked, it is 
often poured into rough containers where they harden relatively quickly – often 
resulting in cracking or crazing of the material.  This process, wherein the 
glass is chemically created to the correct formula is called Melting.

The next step in glass making generally involves re-melting of the glass and 
mixing it to improve its homogeneity and clarity – this process is called 
generally called refining.  Because the goal in this step is make the glass 
have more uniform and perfect appearance, not to make chemical reactions which 
will change the compounds making up the glass, this is generally done above the 
melting point of the glass but well below the temperature below that at which 
the Melting was done.  After the glass has been melted and stirred – and 
sometimes has an inert gas bubbled through it – it is generally poured into 
heated molds of roughly the desired final shape.  The molds are often made of 
iron or steel, but may be made of graphite or platinum if the glasses are 
aggressive in attacking iron or melt at very high temperatures.  The molds are 
heated so that the glass doesn’t solidify immediately and crack, but slowly 
cools into a solid, transparent mass.

With the glass in the desired shape and very uniform internally, the only thing 
left to do is to remove any mechanical stresses that may have built up inside 
the glass while it solidified – sort of like the stresses that occur in water 
when it freezes to ice and sometimes exert enough force to cause it to buckle.  
This process, in which the glass is brought to a temperature below where it 
begins to noticeably soften and allowed to remain for a long period of time 
while the atoms rearrange themselves by very tiny amounts to relieve any 
internal stresses, is caused Annealing.  If a glass is not well Annealed, the 
residual stresses are generally enough that if you produce a tiny crack or even 
tap it lightly with a sharp edge, the glass may shatter in millions of tiny 
pieces that fly everywhere.

After Annealing, the glass can be further shaped by cutting or grinding into 
final form.

While some of the steps can be combined – it is possible to Melt the oxides in 
a single furnace, then reduce the temperature slowly and Refine it in the same 
furnace, then reduce the temperature slightly below the softening temperature 
and then allow it to harden, the furnace design becomes pretty tricky and it’s 
hard to produce something that’s useful.  Such a furnace would cost several 
thousand US$, at the very minimum, which I consider WAY TOO EXPENSIVE for a 
home project.  And using many furnaces, all of which need very good temperature 
control, is TOTALLY OUT OF SIGHT EXPENSIVE.

With all of the above as introduction, let me briefly answer your questions 
directly:

1.  How can you make glass using household materials?  You could probably toss 
some borax and sand and lime together in a steel or ceramic pot and try to heat 
them with a torch to see if you could get them to melt, but even if you did I 
think it would be nearly impossible for you to make them into something useful 
at home.  Even if you tried to use your home stove, you couldn’t achieve the 
temperatures needed to keep the glass soft enough to work but high enough or 
controlled enough to cool it in a way that would produce a usable, safe 
product.  IN OTHER WORDS, DON’T TRY TO MAKE GLASS AT HOME BECAUSE YOU’LL MAKE A 
BIG MESS AND HURT YOURSELVES OR OTHERS.

2.  How can you make a puff of smoke?  This is unrelated to glass making, but 
the best bet would be to go to a magic supply house and purchase a quantity of 
flash powder which is commonly used for this purpose.  As a physicist, rather 
than a chemist, I’m not sure exactly what flash powder is made of – probably 
some powdered flammable metals – like aluminum and magnesium – and something 
like gunpowder – which would ignite the whole mass if it is struck heavily 
against a hard surface.  AGAIN, DON’T TRY TO FORMULATE OR MIX YOUR OWN FLASH 
POWDER BECAUSE IT’S TOO DANGEROUS TO HANDLE SIGNIFICANT QUANTITIES OF THE 
MATERIALS INVOLVED – YOU’LL PROBABLY HURT YOURSELF OR OTHERS, AND COULD DAMAGE 
NEARBY EQUIPMENT OR FURNISHINGS.  Buy and use only the commercially available 
material, and be sure to follow the directions carefully.

3.  How can you make glass shatter without hurting anyone?  This is actually 
easy:  don’t use glass, use the materials that are made for the entertainment 
industry to simulate glass in action films.  Studio supply houses should be 
able to supply it to you in forms that might be useful:  cups, glasses, flat 
plates, and so on.  I’m not sure exactly what material is used – I’ve heard 
from others at various times that it’s a crystallized sugar or polymerized 
(made into plastic) form of vinyl alcohol product that just kind of falls apart 
when it is struck by a hard object, producing a few large chunks without sharp 
edges and a bunch of powder.  THE KEY HERE IS TO USE THE COMMERCIAL MATERIAL – 
IF YOU TRY TO MAKE IT YOURSELF, YOU’LL PROBABLY SPEND AS MUCH FOR MATERIALS AND 
EQUIPMENT AS FOR THE RIGHT GEAR AND YOU RUN A BIG RISK OF GETTING IT WRONG AND 
GETTING HURT.

While I don’t think you can sensibly make the glass at home as you suggested, I 
think that my recommendations should allow you proceed to develop your magic 
trick in a safe and convincing way.  I hope that you also have learned a bit 
about glasses – which are everywhere, but which almost nobody understands.

Thanks for the question!


Steve Guch
Physicist, Apopka, FL, USA