Wednesday, 21 December 2016

Diurnal Firing Practices

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.  Many suggestions can be 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 convenient time 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. 

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 through 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 lose 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.