Wednesday, 12 November 2014

Observation


It is the monitoring and observation of the effects firings as they progress that allows confidence in setting firing temperatures and schedules. Although we all have busy lives, planning the firings so you can watch at the forming temperatures enables you to develop your firing practice much more rapidly than firing and waiting to see what comes out the next day. It means that in a single firing you can pretty accurately determine the temperature you need for firing that type of piece, rather than an number of separate firings.

You set your schedule - for the best guess that you can make - at the required temperature, rate of advance, and soak to achieve what you need. At about 50ºC to 20ºC (depending on your certainty) before the set point, you begin peeking to see what the glass is doing. When the glass has achieved the desired result, you advance to the next segment. You of course, have already refreshed your memory on how to do that from your kiln manual.

There is a method of opening and closing kiln to be safe and avoid disturbing the contents. Any observation ports should be opened first. The lid/door should be opened slowly and only enough to see what you had already planned to look at, to determine whether it is ok or a decision is needed for some other action. This opening should be only a few seconds. The air temperature will change dramatically, but the glass temperature will lag behind significantly, so a few seconds with the door only cracked open will not damage the glass at most temperatures. The exception to this is the annealing range – generally around 520C to 400C. The kiln should not be opened at these temperatures so that there is no disturbance possible to the steady and even annealing of the glass.

At temperatures above the annealing, you need to have protective clothing. At the minimum you need natural fibres such as cotton or wool, and eye protection. It is important to check with your hand the amount of heat coming from an observation port before moving your face toward it to look into the kiln. When the kiln is being opened even for brief periods, you should protect you eyes from the infra red given off by the kiln's interior. You should have something to protect your arms and chest too.

Always when raising and lowering the lid – or opening and closing the door – do it slowly to avoid creating puffs or billows of air moving through the kiln which might disturb the pieces at low temperatures or move debris over the hot glass at the higher end of kiln forming.

If the glass has not achieved what you want by the end of your soak, just extend the hold until the effect is achieved. You will have reviewed how to do that from your kiln manual before starting the firing. When the glass has achieved the effect you desire, advance to the next segment of the schedule as the kiln manual directs.

You then record the schedule including temperatures, rates, times, effects, etc. You should include a description of the project and its dimensions and nature e.g. full fused, tack fused etc. You will also want to include what this was fired on, what kind of mould – include its description. This will give you the reference for that nature of project for the future without needing to guess.