Annealing

In glass bead making annealing refers to the process by which the glass is heated up to within the annealing range of the particular glass that was used to make the bead. It is then held there for a specified amount of time (depending on the size of the piece) and then cooled down gradually at a constant rate (for example 1°C per minute). This eliminates the stresses within the glass that were introduced in the process of making the bead.

This is because Glass is a very poor conductor of heat and as it cools it does so unevenly, unless cooled slowly. This means that while the outside of the piece may have cooled below the strain point the core of the piece may well still be much higher (maybe even still above the softening point. The upshot of this is that as it cools stresses build up.

If these stresses are not removed from the glass then it may cause the bead to shatter or crack in the future. This could happen at any time, even years in the future.

(In silversmithing annealing is the process of changing the structure of silver to make it workable!)

Why you need to anneal your beads

Here you can see the effect of not annealing your beads. By using polarising filters to show the stress. The bead on the right has not been annealed, you can see the stress in the bead as the blue and orange coloured parts, the bead on the left has been annealed and shows no coloured sections (note that the dark areas are just shadows and reflections)

If you are planning to make glass beads to sell then they must be annealed. This means that the bead is more durable and less like to shatter ruining the jewellery item that has been made

How to tell if your beads are annealed

There are a variety of tests that you can use to test if your beads are annealed some more "scientific" than others.

Bounce test

This means you can bounce your glass bead on a concrete or tiled floor and it will remain intact. This is not truly recommended although dropping does occur regularly by accident!!! This may lead to slight chipping of an otherwise totally acceptable bead!

Cold to hot test

This involves making your bead very cold i.e. putting it in the fridge and then transferring it rapidly to hot water. This is NOT recommended as the glass bead may be perfectly annealed but the thermal shock may cause it to shatter!

Polarising lenses

This is probabaly the most reliable method of checking your annealing schedule. This involves holding the glass bead between two polarising lenses up to a light source and looking for stresses in the glass. These show up as coloured areas in the glass. (see Media:Bead_Annealing.jpg above) Please note: it can only be done on transparent beads.

What Temperature should you anneal beads

This depends on the glass that you are using and it's coefficiency. The manufacturers of the different glasses will hold information about the strain point and the annealing range of glass which should help you to develop annealing schedules on your kiln

For How long should you Anneal Beads

It is not possible to over anneal glass, but you can certainly under-anneal.

The length of time needed to anneal glass is dependant on the size of the piece at it's thickest part. The bigger it is, the more time is needed, as the bigger the piece the more time it takes for the glass temperature to stabilise in the kiln, until ultimately the entire piece is at the same uniform temperature.

The rampdown rate is also related to the size of the piece, as larger pieces require a slower ramp down towards the strain point

As a rule of thumb for beads no larger than an inch or so, you should anneal for an hour.

FAQ

I'm impatient... When can I remove my beads from the Kiln?

When your kiln temperature has dropped below the strain point of the glass you are using it is safe to drop the temperature much more quickly. You still need to be careful as your beads could suffer thermal shock, in the same way that a glass rod can shatter if you just plunge it into the flame without warming it up, this is different from stress cracking.

When the kiln is well below the strain point (at around 200°C, maybe higher) you can part open the door of your kiln to speed the process of cooling, as the natural thermal capacity of the kiln will still stop the beads from cooling too quickly. Remember below the strain point the only damage you can do to your bead is thermal shock cooling them quickly now will not affect the annealing process.

Once the kiln is below 100°C it is possible to to open the kiln door fully, and allow the kiln to drop much more quickly.

Once the beads are at a safe temperature to handle (less than 50 - 60°C ) You can carefully remove the beads and admire your work. (remember they may be hotter than you think, be prepared to put them back in the kiln).

Please be aware that while the beads are still warm keep them away from any cold drafts as although it is very unlikely there is still a chance they may thermaly shock.

Please remember that it is better to be safe than sorry. If you are at all concerned or have just made the world's best bead, then you need to learn some patience, and be a bit more conservative. Maybe even waiting till the morning before opening your kiln.