Hello All,

I have a question that I was hoping to get some help on, regarding heating up my kiln, and how long to keep the piece in, in light of the facct that the temp goes down when the door is openned and takes about a minute to get back up to 1450F temp.

I have a Rio Grande PMC kiln.

For the first segment, I set:

ramp= full, temp= 1400F, hold= 0

(at this point it overshoots the temp to about 1425F or so, and then ramp slows down to continue on up to second segment as below.)

Then for the second segment, I set:

ramp= full, temp= 1450F, hold= 0 (at this point it overshoots the temp to about 1470F).

so, I open the door, and put the trivet in at about 1470 (target is to fire at 1400-1450 max), and the temp drops about 150 degrees F, to 1320F)

it takes about a minute to get back up to 1450F

(so, for about a minute of the estimated 2 minutes in the kiln, the piece is not at the 1450F.

so, my questions are:

- does the estimated 1.5 to 2 minute clock start when the door shuts (at 1320F)

- or, does the clock start ticking when the temp gets back to 1450

- in other words, does the piece have to be at the 1450 for the whole 2 minutes?

(...I know that I am not supposed to just use a time such as 1.5 to 2 minutes, but rather should visually check the piece to see what stage it is at...but, just so that I can understand the concept a little better, let's just say 2 minutes is the right amount of time for this example...)

Any help would be greatly appreciated!

p.s. I just re-fired my signet ring in an attempt to heal the cracks, and was confused about the temp ups and down, and finally left it in for the full 2 minutes at the 1450F, and then pulled it out, and it looks glossy...but I was worried due to the fact that it was sterling silver and the depletion guilding was sanded off in some areas, and it had already been fired multiple times...and now it is sitting under a metal bowl to cool down slowly, and so I thought I would take this time to post this question.

I hope I am making some kind of sense...!

Best Regards,

Julie

Welcome.
I am a beginner. I test enamel 100, 200 - 500 times. Then I know how to burn.
Listen to the advice of Edmund because he is a master.

Yours Leszek

Hi Julie B! Now it's my turn to give back a little for all your great info :-)

I don't know if you are firing predominantly jewelry but I am so I'll tell you how I fire- and this works for me. I'm sure there are a myriad good ways to do this, this is just mine :-) I don't have programmable kilns so I tend to let them warm up until  they are about 1600F and then dial them back down so they stay hot, about 1550 to 1600. My kilns are larger so I'm accounting for a larger drop in temp when a door is opened. Basically I'm setting my base kiln temp a bit hotter than I'd fire to allow for the temp drop to be no lower than what I want to actually fire the piece. I try not to fire below 1450 unless I'm using a specialty enamel like painting enamels or if I'm doing a lustre finish. I tend to fire between 1450 and 1500 (all my temps are in Farenheit), keeping the kiln from rising any higher by cracking the door as needed.

You probably don't do this either but I never walk away from my kiln while I have a piece in it. I stand there and watch that temp like a hawk and adjust throughout to maintain a constant temp. I always tell my students adjust the time not the temp. If you establish a good temp to keep as a constant you'll have eliminated one variable in the firing process- makes things a little more predictable. I do find that 1-2 minutes for small pieces is usually sufficient as long as you aren't clearing oxides out of a transparent on copper but I do usually check the piece starting at 1 min. 30 secs. and then fire to 2 if needed.

Sorry this is a bit rambly but I hope that helps some. If the kiln is too cold, you will get cracks in the enamel- I think that 1320 temp you cite is too low to put the piece in, personally. I would recommend running the kiln hotter than needed to account for the drop- I'd try to run it so that after the piece goes in the kiln is reading no lower than 1400. A minute is half your firing time which again I think is too long to be ramping up from that low temp. If the kiln starts to go above your 1450 max, then I'd adjust the temp with the old fashioned cracking the door technique.

I second Leszek. I think Edmund would probably have the definitive answer!

:-)

Hello Jewel!  

Thank you (and Coral at EnamelWorks Supply Co) so much for your advice, it was very helpful!

so!  I set my rio pmc kiln to 1500 F

and when I opened the door and put the piece in, it dropped 100 F, to 1400

and within a few seconds ramped back up to 1450.

then I used your "crack the door" technique to regulate the temp, and it worked like a charm!

(fired to full glossy at 1 min 30 sec)

I need to test shorter times to get a feeling for the orange peel next.

And here is an additional thing that I was doing wrong, that I figured out after testing your technique out with an empty kiln first (where the temp behaved as you said)...and then trying to fire a piece (where it took 2 minutes to get to 1400 again)...

since I had not yet received my trivets, I was using a homemade jig on a solderite kiln shelf, and putting the whole unit in...(the cold kiln shelf was suckin up heat!), and although the initial tempurature drop was only around 150 F, it was taking almost 2 minutes for the kiln to recover to 1400 F...due to the cold kiln shelf!  This is what was initially confusing me the most, and probably distracting me from thinking the problem through better!  

So, I heated up the kiln, with the kiln shelf already in, then get to temp, and only had to put the homemade jig in.  This time, the temp recovered in a few seconds!

Also, previously, before your advise, when I tried to increase the heat to account for the temp drop, the kiln temp kept climbing past the target temp, and in my nervous state I did not even think about cracking open the door to regulate the heat!  I just assumed the pyrometer was supposed to take care of all of that, and was thinking "I am stuck between a rock and a hard place!""...

So, thank you for the "double date" with my kiln!  I think I am slowly getting to know it a little better!

Best Regards,

Julie

Hi JulieB,

Ahh, yes putting in such a large thermal mass as a cold kiln shelf will also dramatically affect the ability of the kiln to recover. Glad the info was of some help! Edmund also posted some firing info on the grinding thread which is also helpful. He rightly pointed out that everyone has to get used to how their kiln behaves (they all have their own personalities :-) ) and take into account where the pyrometer is. If I recall correctly, he figures a 100C difference between his firing position and the pyrometer reading in his kiln. I do take that into account for my firings as well and do a little mental guesstimating as to what my firing position temp is versus what the kiln is reading (my pyrometers are at the back of my klins as well). It may be a small difference but when you have a particularly tricky firing it's good to keep that kind of thing in mind. :-)

Julie, 

Here are some random thoughts:  You will also find that you need to adjust your time based on the size of your piece.  A 1/2" circle is going to fire a lot quicker than a 5" piece.  Don't be afraid to peek in and check you work, it's not like baking a soufle.  They were doing this ages ago with very primative equipment, and still produced beautiful work.   One of my teachers used to wait until the kiln recovered to the programmed temperature, and then she would count to twenty before taking a look. Worked for her.  If the trivet is starting to get pink, it's probably time to take a look.  It's my understand that underfiring (except for the first and last layers)  helps in reducing the chance of bubbles appearing. Thompson's Workbook has the softening and flow temperatures for the different enamels, and I find it helpful to consult that when choosing colors for a composition.  It avoids the possibility of a very soft enamel bubbling up through a harder one or bleeding into an area you don't want it to go.  I bet you do beautiful work~ have fun!