Tech Sheet #1-
Glass and Annealing Glass by Zenia See
Making
glass beads requires two things to be successful- a torch, and the glass. Glass
for flameworking is endless in its options. Beads can
be made either with pre manufactured rods or sheet glass that has been cut into
strips and fire polished.
The Glass
Rods come
from a series of companies- Moretti (Effetre), Bullseye, System 96 (Uroboros and
Spectrum), Borosilicate, Pyrex, North Star, Lauscha, Satake. Rods vary in diameter
depending on the batches made by the manufacturer but range between 4 and 7-
8mm. Most companies also have lines of frit and powders as well as thinner
stringers to work with. Bullseye Glass, a major
manufacturer of fusible sheet glass and sundries has a tremendous line of rods
that are compatible with all of their sheet glass, frit, powder, dichroic glass and other accessories! Companies such as Moretti are also coming out with sheet glass to make larger
pieces. Each company has a different COE. Make sure to label all of your
companies and their COEs and don’t mix them!
COE
The
COE (coefficient of expansion) is the rate at which glass expands or contracts
as it is heated or cooled (COE is a very small measurement to the power of
-7!). This is important in working with hot glass because the glass needs to
cool and contract at the same rate to eliminate any stress in the bead. One
rule of thumb is to make sure that while doing any hot or warm glass work is
that all of your glass is tested compatible and that all pieces that are being
used together have matching COE. The worst feeling is making something and as
soon as you take it out of the kiln is having it break- but you can avoid
this… just use the same COE for your project and it will all be fine.
|
Company |
COE |
|
Bullseye |
90 |
|
Moretti |
104 |
|
Lauscha |
104 |
|
System
96 |
96 |
|
Borosilicate |
32 |
|
Pyrex |
32 |
Types of Glass
There are two so called
“types” of glass that are manufactured specifically for flameworking and beadmaking. They
are called Hard Glass and Soft Glass. They are categorized by the materials
they are made up of and by their COE. The higher the COE the softer the glass
usually is.
Glass
is not a solid or a liquid but a vitreous substance (refer to FigHelper #7 where MIkey tells us
about this fourth state of matter). The way the molecules are lined up they
look like they are in a liquid state because of their random arrangement. Due
to this, the bonds are all different lengths thus requiring more or less heat.
So, the bonds are slowly broken slowly changing the glass from a solid to a
liquid. Soft and hard glasses are unique from one another in many ways.
Hard Glass (aka Borosilicate or Boro)
Borosilicate
glass contains boron oxide. The boron molecules are smaller in size and due to
this the COE is very low- only 32! Boro is a very
forgiving glass; it is very stiff and slow to work with. It requires a very hot
flame because of the small bonds that need a lot of heat to be broken. Boro is also very forgiving in the cooling process, because
it has such a low COE there is little contraction so even while working with Boro you can stop and put it down without fear for it
cracking. The colour palette is not very broad but
the colours that are available are very different
from that of soft glass. This is so because the metal oxides that are used to colour soft glass would burn out in the hotter flame if
they were used for colouring Boro.
With Boro you could technically get up to 5 different
colours out of one rod just by the type of flame
used! Other companies that produce hard glass or Borosilicate based glass
include Pyrex, and North Star. (Note: Scientific Lab equipment is made out of
Borosilicate hard glass tubes.)
Soft Glass
Soft glass is what fuser
typically work with. It has higher coefficients and
requires lower temperatures to manipulate. The dominant company that makes rods
for soft glass is Moretti (Effetre). It has a
coefficient of ‘around’ 104 and has a broad range of over 170 colours! Bullseye Glass, a long
time stained and fusing glass manufacturer now has added a line of torch rods
approaching 100 colours! According to some
professional beadmakers they really enjoy Bullseye Rods because it is just stiff enough for
sculptural work! Soft glass is a Soda-Lime based glass and is coloured by the use of metal oxides. The metal oxides
absorb certain wavelengths of the visible spectrum showing only reflected
wavelengths. Some metal oxides that are used include cobalt, gold and copper.
Soft glass requires less heat for the same results as Boro.
It is much more malleable and easier to work with. The soft glass stays soft
longer and gives you more working time out of the flame. Soft glass is
recommended for beginners because it is very forgiving and the long working
time is great for detail and learning. One thing about soft glass is that
because the COEs are all so high if they cool to
quickly out of the heat they will crack or explode. So annealing is very
important in soft glass!
Annealing
When a bead is formed in the
torch it is all very hot, now when you pull the bead out of the torch and you
feel the surface get cold, the inside is still actually very liquid and very
hot. Because the “skin” of the bead cools and contracts (shrinks)
and the inside is still hot, the bead starts to build up stress and if this
happens too quickly the bead will explode or crack. This is important to take
note of because if the bead does not crack or explode now it might do so at a
later date. There is one way to avoid your works of art from cracking and that
is by annealing (slow controlled cooling). To properly anneal beads a kiln is
required. The annealing process keeps the skin of the bead and the inside of
the bead at the same temperature and brings the temperature of the bead down
slowly and all together to avoid any stress in the bead. You just have to make
sure that as soon as the glow is out of the bead you place it in the already
hot kiln. Annealing temperature for most soft glass (including BUllseye and Moretti) is between
960 and 990F. If you are spending a day beadmaking
just keep popping them into the kiln and when you finish for the day leave the
kiln on for between 45 minutes and an hour to let the beads “soak”
and all reach an equal temperature throughout the bead. When the beads are done
soaking the easiest way to have them gradually cool down is just to turn the
kiln off (each kiln is different, so read the manual) and DON’T OPEN IT!
The cold air that enters can cause the beads to thermal shock and
explode/crack! Thermal shock is when the bead is exposed to too much cold air
at once and the stress between the cold skin and the hot insides cause the bead
to break. Thermal shock can also occur when putting a cold rod into a hot
flame. If you do not slowly heat the rod by wafting it in and out of the flame
until it starts to soften it may ping and chip. This is just too much heat all
at once. This will not be a problem for the quality of the beads because once
the glass is liquid you can not break it. But it may be a problem if you have
pets or young children walking around because the pieces tend to fly. Oh and by
the way watch your arms and hands… they look solid and cold but they are
HOT!