Reckoning heat without measuring it - pottery firing

[Arron]

Hi. I sometimes fire small pottery items in our back yard using charcoal as a fuel. It works OK but the limitation i come up against is that it’s all driven by guesswork. I don’t have a pyrometer so the problem is reckoning heat to make the process repeatable.

The only way I currently have to measure temp is to drop in small balls of aluminium foil which I have read melt at 660 celsius. That temperature isn’t much use however so I usually take the fire a long way above that and indeed the pottery comes out hard and strong, but to what temperature I have no idea.

I expect I max out in the 800-900 range.

This is complicated by the fact that I dig my own clay so I don’t have any parameters for it.

So anyone know any ways I can measure or guesstimate heat? Any other substance that melts in this range that I can use to gauge heat?

Assuming those into foundry and blacksmithing might have something to add.

Cheers
Arron

[Wrongwayfirst]

Try this

High Temperature Non-Contact Thermometer & K-Type Input - ICQM7430

cheers

[BobL]

Most of the no-contact type infra-red thermometer with Type thermocouple attachment only go to 600 or 800º

You need to read the blurbs carefully to make sure that they go to at least 1200º or 1000ªC
There are heaps on ebay and here is one for about $50
Digital Display Thermometer Temperature Meter Sensor with K-Type Thermocouple | eBay

Some that say they will read to 1300º have thermocouples with plastic handles which are not going to last when they're anywhere near that sort of temp

[Arron]

Most of the no-contact type infra-red thermometer with Type thermocouple attachment only go to 600 or 800º

You need to read the blurbs carefully to make sure that they go to at least 1200º or 1000ªC
There are heaps on ebay and here is one for about $50
Digital Display Thermometer Temperature Meter Sensor with K-Type Thermocouple | eBay

Some that say they will read to 1300º have thermocouples with plastic handles which are not going to last when they're anywhere near that sort of temp

Thanks Bob. I’m not familiar with these. I assume I would just poke the end of the probe into the firing chamber and place the meter itself as far away as the cable would allow. I presume I can leave it in place and just read the meter as needs require.

Looking for one despatched locally, would this one do the job ?

New K Type Digital High Temperature Thermometer Pyrometer and Probe 1300℃ F | eBay

I also presume if the probe proves to be not up to the task then I can replace it with another one - like this : K Type Thermocouple EGT Temp Probe Temperature Sensors Thermocouple 1 Pcs | eBay

Cheers
Arron

[BobL]

Unless you lquickly make a measurement and then remove it, that TC has a short probe that will quickly conduct heat back to the plastic insulation and melt it making a mess.
The probe should be longer and/or have fibreglass insulation which is not as affected by heat. It also means you can get the meter away from the heat source.

[Arron]

Ok, I bought an inexpensive locally-available digital thermometer. It comes with a thermocouple which has plastic so I can either read very quickly or upgrade to a better thermocouple.

It’s a cheap unit but it should be OK - I’m not interested in great accuracy or do this very often.

Thanks for the help Bob, and the suggestion Wrongwayfirst.
Cheers

[Arron]

Well my thermometer and probe arrived a few days ago so this morning I gave it a test run. I drilled a hole in the back of a hibachi barbecue - a bit too small to maintain an even heat within but I had very little charcoal on hand.

It worked well. The main limitation is that it takes a while to get up to a true reading and if the plastic on the probe is not shielded from the heat then it softens fairly quickly. Using it in the hole I drilled means that I can keep the probe most of the time in the hole but right at the very outside edge where it’s about 600c (which doesn’t bother the plastic) and just push it in long enough to get a stable reading.

Highest reading was 965c. Bisque fire is usually done at 1000c although the sintering stage of the process of turning clay to ceramic actually occurs about 875c, so maintaining the temp at about 900 for a couple of hours produces pottery items that are too hard and tough to be broken by hand. Not vitrified, not glazed and not waterproof of course as that stage needs temps above 1100c and not really practical without a kiln.

Thanks again for the help.
Arron

60C65177-9EA5-4B43-8440-55BCC9268CE5.jpg

[Arron]

This raises a question about firing things. If charcoal burns at approx 1000 degrees c, if I have that charcoal burning in a chamber can I raise the temperature of the chamber significantly above 1000 c ? Let’s imagine the chamber is well insulated, has a fan blowing in air, and very precisely calculated vent holes.

I guess when put another way, the question is does containing the heat allow it to build up above the heat at which the combustible material is burning.

Sort of like continually producing a gas in a confined space will raise the pressure within?

Cheers

[Wrongwayfirst]

I am def no expert but forcing air onto charcoal would increase the temp. That is the extent of my knowledge, add oxygen more burn.

cheers

[Skew ChiDAMN!!]

I guess when put another way, the question is does containing the heat allow it to build up above the heat at which the combustible material is burning.

Yep. Appropriate insulation will reduce radiant/conductive losses to levels below the heat input, resulting in increased temperatures.

I don't know what you'd call significant, but I know of charcoal fired kilns that are run @ about 1250 deg C.

[Arron]

Yep. Appropriate insulation will reduce radiant/conductive losses to levels below the heat input, resulting in increased temperatures.

I don't know what you'd call significant, but I know of charcoal fired kilns that are run @ about 1250 deg C.

Yep, that’s significant.
Thanks
Arron