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This information is offered
to provide a basic working knowledge of the Effetre Glass palette
and some of its limitations.
When working with any glass it is important
to know its compatibility. Coefficient of Expansion or COE, is the
term used for the measured expansion and contraction rate of a
type of glass based on the percentage of change during the heating
and cooling process. Glass of differing types, (based on the raw
materials used to make the batch), will have different rates of
expansion and contraction. Glass with greater expansion
capabilities has a higher COE rating. Glass that is of the same or
very similar COE and that has the same basic raw ingredients in
the batch is compatible and thereby workable with another glass
made from the same basic ingredients. To be compatible glass must
be of the same or very similar coefficient of expansion,
viscosity, and annealing range.
For some applications this
general rule can be broken, but for others it becomes more
important. When making glass beads COE becomes important,
especially when incasing and most often concerning the core layer
of the bead.
For our purposes lets talk about
Effetre glass. This beautiful soft soda-lime glass is made on the
Island of Murano in Venice, Italy. Formerly owned by the Moretti
Family and thus formerly known as Moretti. Effetre glass is most
frequently used for flameworking and glass beadmaking. Effetre
glass has been made for hundreds of years in the same factory, it
was created especially for beadmaking and comes in a wide range of
colors. Effetre comes in 5mm-15mm thick rods as well as sheet form
with a COE of 104-113. Effetre’s color palette is broken down into
six categories.
Transparent colors; COE
104-106
*exceptions, red T076 COE
109-113
Pastel colors (Opaque); COE
104-106
*exceptions, dk turquoise P236, dk
pink P256 COE 109-113
Alabaster colors (translucent,visible lines of trapped air
running length of the rod); COE 106-108
Special colors (hot colors, yellow, orange, red, transparent
ruby, etc); COE
109-113
Opal colors (translucent milky colors); COE 109-113
Filigree colors (core color cased in clear glass); COE
104-106
It is important to note the
wide-range of COE in the Effetre palette when considering making a
cased glass bead. Transparent Effetre glass has a COE of 104-106,
whereas for instance the opal colors have a COE of 109-113. If you
start your base bead with an opal color and then proceed to incase
the color with clear you have class with a higher COE, therefore
greater ability to expand and contract, at the core of your bead
than the casing glass. Nine times out of ten the bead will
break.
You might have had a problem with
cased beads of a certain combination breaking in the past. Unless
there is some other logical explanation such as large bubbles in
the bead the difference in COE is likely the reason. This doesn’t
mean you can never make that beautiful cased red bead...there is a
solution to this irritating problem. Start with a base of COE
104-106 glass. Cover that with a layer of the higher COE glass
that you want to use, and then proceed to case etc to create your
finished bead. You must be certain that the core layer of glass
runs the full length under the second layer. What you have then
created is a sandwich of completely compatible glass with the less
compatible glass floating in between.
Here is a list of many
popular types of glass used for flameworking with the COE and
other information to assist you.
Satake (Japanese
Soft Glass)
Approximate Coefficient of Expansion (COE):
Soda
lime colors: 113
Lead colors: 120
Annealing Temperature: 890º
F
Effetre/Moretti
(Italian Soft Glass)
Coefficient of Expansion
(COE): 104
Annealing range: 920 - 968º F
Strain Point: 840º
F
Softening point: 1050º F
Working Temperature: 1400º F
Vetrofond/Murano
Glass (Italian Soft Glass)
Coefficient of Expansion (COE): 104
Annealing range: 920 - 968º F
Strain Point: 840º
F
Softening point: 1100º F
Working Temperature: 1400º
F
Lausha (German Soft
Glass)
COE: 95 -
105
Annealing Range: 920ºF to 970ºF
Bullseye (American
Soft Glass)
COE: 90
Annealing
Temperature: 940º F
Strain Point: 820º F
Glass Alchemy
(American Hard Glass)
COE:
33.2 +/- 2.0
Recommended Annealing Point: 565ºC -
1050ºF.
Maximum Annealing Point: 600ºC -1112ºF
Strain Point:
840º F
Softening Point: 1200º F
Working Temperature: 1700º
F
Striking Temperature Range: 1150ºF to 1200ºF
Northstar (American
Hard Glass)
COE: 33.2 +/-
2.0
Recommended Annealing Point: 565ºC - 1050ºF.
Maximum
Annealing Point: 600ºC -1112ºF
Strain Point: 840º
F
Softening Point: 1200º F
Working Temperature: 1700º
F
Striking Temperature Range: 1150ºF to 1200ºF
Colormax (French
Hard Glass)
COE: 33.2 +/-
2.0
Annealing point: 565ºC - 1050ºF
Pyrex (American
Hard Glass)
COE: 33.2 +/-
2.0
The following three companies make
what is known as Reduction Frit. Reduction Frit was originally
used in glass blowing but now is often incorporated into
flameworked glass beads made of Effetre and Vetrofond glass. While
the COE is not the same as Effetre, it is used in such small
quantities that no problems occur as long as the beads are
properly annealed.
Q-Colors by Reichenbach
German Soft
Glass COE:91-94
Kugler by Friedrich
German Soft Glass COE: 89 –95
Wiesenthalhutte by
Ornela
German Soft Glass COE:88-92
Question - What should you do when you don’t know the
COE of a type of glass but want to work with it? Answer -
Try a Compatibility Test!
COMPATIBILITY TEST:
For flameworking, the most commonly used is the Pull
test, or Strand test. Heat two rods of glass, attach together
overlapping them one inch, heat together without mixing or
twisting, then pull into a thin straight cane. When cut off the
rods, if the cane remains straight the two glasses are compatible.
If the two glasses differ in linear expansion, the cane will be
curved. The glass of greater linear expansion, (higher COE
rating), will be on the inside of the curve because of its greater
ability to bend. The greater the curve, the greater the difference
between the two glasses. In some cases, if the glass is of great
difference, one rod will pull out while the other cools thus not
pulling as much, if at all.
ÓApril 14th
2004 Written by Kimberley Rosaleen Osibin – Create Beads!
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