It is most
common for people to fire overnight so they can see their piece(s) the next
morning. This is a poor practice for novices. Not simply a lazy one. It is a practice that
leads to use of others’ programs and practices, rather than building on one’s
own experience and practice. Others’ programs are used because they were
successful for them. They may not be
successful for you. The number of failed projects that are discovered when the
kiln is opened, show that it is often not possible to transfer another’s
schedule to your project.
The ability
to fire while you are absent is a great advantage to kiln forming
practices. The widespread use of the
controller has brought many advantages to kiln formers, not least that they can
get some sleep and have a social life. They no longer need to be beside their
kiln all the time it is firing. The
controller has also made it possible to set the ramp rates and soaks without
calculations. And without having to set
periodic alarms to remind us to check the kiln to see if it is advancing at the
correct rate.
Before
controllers it was necessary to sit beside kiln to watch what was happening and
adjust the ramps and soaks to conform to what was planned. It was also necessary to observe how the
glass was behaving and adjust the power input accordingly. Now we can set the
controller to give what we hope will be a good result. We find out when we open the kiln in the
morning whether it is right or not.
I am not
advocating returning to the days before controllers. I enjoy my sleep and social life too much for
that.
I am advocating the use of a feature almost all controllers have - the Delay function. On most controllers, it is the first thing that comes up on the display. We mostly ignore that and proceed to the first ramp. We set the controller to fire immediately, so that it will be done overnight and we can look in the morning or when we come back from work. That way all the waiting for the piece to be finished can be eliminated. We can go to work or to sleep knowing that the firing will be done when we can get back to the kiln.
This
practice leads us to miss the real learning process that is available by
observing the process of the firing.
Observing the firing can tell you when your slump is done, when it is
slipping to the side, when it breaks, when more time is needed, when more heat
is needed – almost everything that people ask questions about their slump – or
in other instances, the fuse or melt.
People ask
what temperature they should use for the kind of tack fuse they want, and many suggestions are made. Trial and error will eventually tell which is
the right combination of rate, temperature and time for the result you want. Observation
during the firing will tell you immediately when the temperature is high
enough, or the soak is long enough. As
you peek into the kiln through the observation ports you can advance to the
next ramp when you have achieved the look you want.
You do have
an observation port, don’t you? It is one
of the essential features to be included in a kiln. If you don’t have one, you
can open the lid or door momentarily to observe the state of the glass in the
midst of the firing. You could make an
observation port by drilling through the casing and insulation. You then place fibre blanket or a formed
piece of kiln brick in the hole when not in use for peeking into the kiln. You will not change the performance of the
kiln by doing this. Of course, if you
have side elements, this retrofitting of an observation port is risky.
“I need a life. I have to work. I have to sleep. I can’t be around my kiln all the time.”
The legitimate responses to the idea that you should be around to observe the work at critical temperatures are that “I need a life. I have to work. I have to sleep. I can’t be around my kiln all the time.” This is where the Delay function comes to your aid. You can use the Delay function to make sure the firing is at the critical point for observation at a time that is convenient for you. This way, you do not disrupt your normal life. Your social life can continue and you can get some sleep too.
An example
will help understanding how you can make use of the Delay function.
If you have
time before you go to work, you can set it so that the firing comes to the
critical point about an hour before you have to leave for work. Or if it is better for you, you can set it so
that time for observation is after you get home from work, or after dinner,
etc. Even if you don’t have a day job,
you can use the Delay function to make sure you will be able to give the kiln
the attention it needs at a time convenient for you.
How do I do
this? It is a setting of the amount of
time to elapse before the kiln starts to fire on the first ramp. Most programmes have firing times for each
ramp. You select the cumulative times up
to the end of the ramp for the observation to begin.
This does not need to be difficult
This sounds
complicated? Not really. It is a bit of arithmetic, though. Add the times for each ramp together to get
the time the kiln will take to get to the observation temperature and
soak.
E.g.:
200C/hour to
630C for 30 mins =3.15 hours plus the
0.5 hour soak. (divide the target
temperature by the ramp rate, in this example 630/200=3.15 hours or 3 hours and
9 minutes). Don’t include the soak time
in this calculation as that is the part of the observation that is or may be
variable.
Assume it is
10:00pm and you want to look at it at 7:00am.
This is 9 hours. The kiln needs 3 hours and 9 minutes to get to the
temperature you want to observe the slump.
Subtract 3 hours and 9 minutes from the 9 hours you have and this gives
you 5 hours and 51 minutes to set in the Delay function.
Some
controllers do not allow hours and minutes, but require only minutes. In this case, multiply the hours by 60 and
add the minutes. In the example, there
are 300 minutes in 5 hours plus 51 minutes gives 351 minutes to be put into the
delay function.
In this
example, this will have the kiln at 630C at 7:00 am. Ready for you to observe
the progress of the slump. When the
slump is finished, you can advance to the next segment and head off to work,
allowing the cool and annealing to proceed, and knowing the slump was
successful. The same applies to other
times of the day. You could, for example
load the kiln and schedule the delay to be at the critical temperature for when
you come home from work.
Setting the delay function for an exact tack fuse is a little more complicated.
If you are looking to get an exact tack fuse profile, the schedule will be a little more complicated. Say you want a rounded tack fuse that you think will be achieved at 750C in 10 minutes. The schedule might look something like:
Ramp 1:
200C/hour to 650C for 30 minutes =3.15+0.5 hours =3.65 hours
Ramp 2:
300C/hour to 750 for 10 minutes =0.33 hours (750-650/300) + 0.167 hours soak.
Adding these
two ramps together gives you 3.95 hours.
Here you include the soak at bubble squeeze temperature in the first
ramp, but not in the second, because that is what you are checking on. If it is
7:00am now and you won’t be back until 6:00, that is 11hours until you will be
looking in at the progress of your piece.
So you subtract 3.95 from 11 and you set the Delay as 7 hours, 57
minutes (or as 477 minutes). Then it
will be ready for observation when you come home.
Won't I loose firing time by using the delay function?
You may feel that you are going to lose a firing by using the Delay function. You often can peek into the kiln in the morning to see how things have turned out by using the overnight firing. But there normally is still more cooling down time required.
If you delay
the top temperature until the morning to see what is happening, you still have
the rest of the day for the kiln to cool and be ready for re-loading in the afternoon
or evening. During that time, you can be
preparing the next firing. So you have
not lost any kiln time, but you have gained the knowledge that the firing is OK because of any adjustments you made at the critical temperatures.
If you were
to fire during the day to be able to open the kiln in the evening as your
normal practice, you will lose one firing at the start of this kind of
practice. As you progress with the new
practice, you will find that you do not reduce the number of firings you are able
to complete in a week. Again, you are
preparing the next kiln load while the kiln is cooling.
Yes, it does
require doing things a little differently.
But essentially it moves the kiln preparation on by 12 hours. That’s why I call it diurnal firing. You are just changing by 12 hours your daily
practice. You make things ready for the kiln to fire overnight, and prepare the
new piece(s) during the day. Or prepare
the pieces in the evening to fire during the next day. You still are preparing the next kiln load as
the kiln cools off from the previous firing.
The extra planning effort is rewarded by more rapid learning
This little extra planning is rewarded by the ability to see what is happening in the kiln, so that you can adjust during the firing, rather than having to do a firing again, or in the worst case, completely re-make a piece after a disaster.
You also
learn much faster about the desired programmes required to get specific
results. Instead of doing multiple
firings to find the exact temperature needed for the desired result, you can do
it in only one or two firings. This
saves you lots of time, glass and electricity.
Observation
is really necessary for free drops – aperture drops, screen melts, pot melts,
etc. These require observation to get
the desired results, as their progress is so variable from one firing set up to
another. Using the Delay function will enable you to have the firing at the
stage where observation is important when you are best able to be there to
watch.
The
alteration to your working practices to make use of the Delay function will be
amply rewarded by the rapid learning that observation of the firing
promotes. This essential tool to aid in
designing appropriate firing programs is too often ignored in teaching and
using firing schedules.
Finally, it
allows you to set up programs that are pre-set for your kiln and kind of
work. You will have learned the exact
rates and temperatures and soaks to put into your programs. These become your saved schedules that are tailored
to your practice.
revised 27.12.24
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