Ceramics/Kiln firing

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Question
I am new to pottery and just finished my second firing on my used kiln.  I use mid-range clay and glaze.  I am experimenting with single fire of greenware with glaze applied.  

The first firing almost every piece came out as expected except three small piece (the clay had very small grooves - the glaze on the ridges were fine (shiny) but the dips were not and very dull).  

My second firing just finished.  The clay (bisque) is fine but the glaze was not.  EVERY piece came out with dull, gritty glaze - is looks like the glaze did not melt just turned a hard and powdery looking.  

I looked this up and it appears that I "under fired" per the information I found.  The information also says that I can re-fire.  

I fire according to instructions I found on manual firing.  My kiln shows:  Lo - 2 - 3 - 4 - 5 - Mid - 6 - 7- 8- 9 - Hi on the knobs.  Since I fire to mid-fire 04 to 06 I thought that the "Mid" was at least 05.  I fired up to "7".  

I carefully "warmed" the kiln on low with the lid propped open 1" for two hours.  I shut the kiln lid for another hour then ramped up to 2 for one hour, then 3 then 4 then 5 for two hours each then 6 for one hour then 7 for two hours for a total of 12 hours.  I reduced the heat in increments every hour after that to off.  My question is:  Perhaps the numbers between Lo to Hi do not denote a cone number (ie 04)or specific temperature as I thought.  I am thinking based on the first fire and now the second fire that I under-fired to only a cone 04 at the most - which is what this glaze is rated.  

The question:  To re-fire I know I can skip the warm up as the clay is already dry and bisque.  Since the glaze is somewhat processed, should I keep it at 04 or go up much higher?  Any suggestions?

Answer
I always fire at 06 for glaze. If usual states to 04 bisque?
I would try cone shelf sitters on each shelf. They will bend over and tell you if your kiln is firing correctly? If you are firing 04 use 04 sitters on the shelf. It sounds like you may have an element out? If you know an electrician they can check it in the box outside with a meter.
Also, I hot fire everything. Turn it on high and let it go much easier and I never have any trouble.
Good Luck  

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Debra Flint

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Pretty much everything on ceramics

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I have been teaching for 16 years and I am certified in many different paint companies and techniques. I have been working with ceramaics for over 28 years.

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I have BA in Radiology and many certification from Duncan , Gare, Kimple and many others.

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