Do you need a kiln for lampworking?
there are four common methods of cooling glass beads.
But do they really ANNEAL?
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When you are done working the bead in a torch flame, you can't just toss it off to the side and forget it.
As glass is worked in the flame - stresses are created in the glass,
additionally - glass expands when hot, and contracts as it cools.
If it cools too quickly - then those stresses may break the bead
- or leave weakened stress points in the bead that will break at a later date.
The first concern is to cool the bead slowly to avoid thermal shock....
and the second concern is to relieve stress in the glass.
So, how can you do this?
|METHOD||what happens||does it ANNEAL?|
|FLAME ANNEAL. Move bead out in the flame and reduce temperature slowly. Reduce O2 and allow the bead to bathe in the propane flame lightly.||This may keep smaller sized beads from thermal shocking, as you aren't subjecting it to as large a drop in temperature.May equalize stress in simple beads - but not recommended for sculptural works with more stresses. *||sometimes - not recommended for sculptural works with more stresses. May work well on simple, small to medium size bead - if done properly. Almost impossible with large beads.|
|SLOW COOL - FIBER BLANKET.||Place beads between layers of high insulation factor fiber. This method may keep smaller beads from thermal shocking but may lead to nasty surprises on larger or sculptural pieces. *||This method does not anneal, it is only a preventative measure for thermal shock. NO annealing takes place!
|SLOW COOLING - "Crock Pot" Method. (Using a heated deep fryer (dry) or crock pot with insulating vermiculite. (PLEASE READ!) or perlite.)||This method may keep small to medium size beads from thermal shock - but generally does not work for large or sculptural pieces.At average 400 degrees - this does not meat the minimum temperature for strain/annealing process to take place in the glass.||This method does NOT anneal beads! This is also only a preventative measure for thermal shock. NO annealing takes place! .|
|ANNEALING KILN Placing your glass/beads in a properly heated anneaing kiln, and ensuring proper time and temperatures are maintained during the cool-down and annealing phases.||Using a proper annealing kiln will prevent thermal shock. Maintenance of temperature and cooling schedules allows glass to relax and "anneal" through the cooling phases. This will provide you with the peace of mind that each bead is properly annealed.||YES! Using a kiln will allow you to TRULY ANNEAL your glass.Requires that you have a working knowledge of your glass pecifications for strain point, annealing temperatures, and proper annealing schedules.|
*Many artists use this method of flame annealing even if they
are using a kiln, or may use the slow cooling methods (crockpot/fiberblanket) for holding beads until they are ready to run a whole annealer load of beads. Many artists, myself included, do many smaller beads, remove them from the mandrel after a crock pot or blanket type cooling, and then run them through an annealing cycle from cold start to cold finish. This reduces electricity costs, but risks breakage if used with larger beads. So - I work LARGE beads that need to go directly into the annealer once I have a load or smaller beads ready to run.
Remember .... SLOW COOLING is NOT annealing - it is just avoiding thermal shock.
It is important to note that you still have stress in glass even if you hae flame annealed or slow cooled it successfully without cracking. Stress can still be present in the bead -a polorization scope will show you the stresses in the glass, or they may make themselves known suddenly by breaking days, or weeks, later. Annealing glass is a matter of proper method and proper temperatures.
The"annealing" temperature of each type of glass doe svary- (Moretti/Effrete is about 940 degrees F, and the new Czech lampworking glasses are slightly higher - at about 1000 degrees, borosilicate is even higher).The time schedule at each temperature point should be based on thickest cross section of the bead or glass object. (a typical time for small beads might be 15 minutes at strain point - but longer won't hurt). In other words the larger the bead the longer the annealing time.
REMEMBER - SLOW COOLING is NOT the same as annealing. Please also read resources on ANNEALING SCHEDULES and cycles so that you understand this process.
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