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-   -   About dome "clearing" (http://www.fornobravo.com/forum/f16/about-dome-clearing-12103.html)

kebwi 03-10-2010 09:59 AM

About dome "clearing"
 
I'm a little confused about this dome clearing business.

First, is it the result of the carbon burning off or "turning transparent" as is oddly phrased on FB's webpage on the topic: "This change occurs when the carbon accumulated on the oven dome reaches about 700F, and turns from black to clear."? The carbon isn't really becoming transparent, right? It's burning away, right? I'm just asking.

Second, the quote above and my general understanding of this process seems fairly unambiguous that this transition occurs when the carbon caked on the dome reaches 700F...but then why does it not occur until long after the dome's temperature (per IR thermometer) has exceeded 1000F, like half and hour to an hour later?

Why is my dome 1000F for 30-60 minutes but pure black for so long before it starts to clear? The thin layer of carbon must be well over 700F if the IR thermometer is registering +1000F for half an hour.

I just feel like I'm misunderstanding the process somewhat.

asudavew 03-10-2010 11:36 AM

Re: About dome "clearing"
 
Clearing just means the carbon/creosote is burning off.

I've never checked my oven temp, but mine begins to "clear" about an 1 hour to 1.5 hours into firing and gradually clears down the walls all the way to the floor.

In regards to the temperature, since I don't have experience with a IR therm, are you sure you are getting accurate readings of the apex of the dome?

What readings are you getting on the walls after they burn clear?

kebwi 03-10-2010 11:44 AM

Re: About dome "clearing"
 
Good question. I do like the watch the temps of the sides during the firing. The apex shoots up to 1000F so fast I'm not sure it's really illustrative of the oven's overall status. It is amazing that the sides can be in the 300-400 range while the apex is off the 1000 max my thermometer registers.

I'll try to watch more closely as to the temp of the sections of the dome (apex, side, whatever) where the carbon is clearing. It would be interesting to note.

...although as I said, the confusing part is that temp doesn't seem to directly correlate with the carbon burning off. The apex can be 1000F for a long time and still be black. I'm not sure what triggers the burn-off.

asudavew 03-10-2010 12:22 PM

Re: About dome "clearing"
 
Maybe it is the internal heating of the bricks, and not just surface temp?

I'm not sure either.

dmun 03-10-2010 04:17 PM

Re: About dome "clearing"
 
I think it's like soldering. An IR reading of the flame on your workpiece would read much higher than the melting point of the solder, but the lump of solder just sits there until the metal of the joint gets hot enough for the solder to flow.

I think the carbon burn-off is a really accurate measure of hot hot your oven is. I usually fire mine until there's just a little ring of carbon around the bottom of the dome. It's when the oven is completely clear that I get burned bottoms, at least at first.

kebwi 03-10-2010 04:35 PM

Re: About dome "clearing"
 
Nobody likes a burned bottom.

david s 03-10-2010 11:14 PM

Re: About dome "clearing"
 
Dave ,
Mine performs exactly the same. We have learned that the first pizza is never the best. A bit like the first pancake cooking in a pan. We never bother to swab out the floor, it seems like too much trouble and I'm conscious of losing heat. Perhaps the infrared thermo is being confused and reading the temp of the flame at the apex. Try letting the fire die down and then take another reading. It is interesting how new oven builders get obsessed with the temp. After some experience you just get to know how hot it is. This is the traditional way it used to be done.

asudavew 03-11-2010 06:44 AM

Re: About dome "clearing"
 
Quote:

Originally Posted by david s (Post 84373)
Dave ,
It is interesting how new oven builders get obsessed with the temp. After some experience you just get to know how hot it is.


Exactly, I always know when mine is hot enough.... it's when I burn the hair off the back of my hand. :D

kebwi 03-11-2010 07:32 AM

Re: About dome "clearing"
 
Well, okay. Thanks. From a chemical or physical point of view, I was just a little confused, but from a baker's point of view, I admit it doesn't matter too much.

Thanks.

shuboyje 03-11-2010 11:02 PM

Re: About dome "clearing"
 
In my experience it is a matter of balance. If I have a big fire going in the oven the dome will never fully clear. The fire is producing soot faster then it is burning off. As soon as I push the coals aside and get the oven in order to cook the dome clears rapidly.


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