PTCR measuring rings quantify both time and temperature of the glaze firing: heat work. Why do I think that’s so important to know (and to measure)? There are several reasons for this…

But let me start with what exactly PTCR measuring rings are. PTCR stands for “Process Temperature Control Rings”, so rings to get control over your firing temperature.

And what do you get out of it as a potter? I would like to explain that in this blog.

What are PTCR measuring rings?

They are rings of 2 cm diameter, made of ceramic material, just like Orton cones (Seger cones), clay and glazes. If you fire them in the kiln, they shrink, just like ceramics. But they don’t just shrink, they shrink to the nearest 0.01 millimeter at a certain temperature.

The rings are for sale in packs of 15 pieces, just like a roll of peppermint. But these are not white, but have various colors (and they probably do not taste good either).

PTCR rings are available in the Netherlands at Keramikos, but also elsewhere in Europe at the better ceramic suppliers (and who doesn’t stop by during their holiday).

How do PTCR measuring rings work?

How exactly do they work? It’s very simple. First, you need to choose the right type for the temperature you want to fire. That is the pink PTCR-LTH ring if you fire above 1000 ^oC, but below 1250 ^oC. If you fire higher, take the green PTCR-STH ring that can be used up to 1400 ^oC (see also table below).

Then place a number of these rings in the ceramic kiln, exactly where you want to measure the temperature. Why more than one? So that you can check the temperature in different places. So a ring on the upper kiln shelve, the bottom one, in the middle etc.

After firing, you accurately measure the diameter of the rings (millimeters to 2 decimal places). This can be done with a digital caliper or the “PTCR Micrometer” (which measures up to 3 decimal places).

Then take the table of the relevant PTCR type and “Powder Batch” number. The “PB” number is on each ring and must match the table you are using (so make sure you use the correct table).

Finally, read which temperature corresponds to the relevant diameter that you have measured. And voilà, you have very accurately the firing temperature of the place where the ring was located.

Pyrometer versus PTCR

Okay the rings work simple enough, but why would you use them? Surely the pyrometer connected to the kiln controller also indicates very accurately at what temperature I am firing? Well that’s less true than you think.

Pyrometers measure only temperature

Ceramic glazes are fired just like a cake at a temperature and time, which is called heat work. How fast or how slowly you fire a glaze at the highest 100 to 150 degrees C has a major influence on the melting of the glaze.

If you fire very quickly, the glaze will have melted less than if you do this very slowly. The pyrometer only measures the temperature in the kiln, but the PTCR measuring ring records the temperature and time of the entire firing.

Measuring pyrometers in one place

In most ceramic kilns, the temperature is only measured in one place, usually in the middle. But kilns do not fire at the same temperature from top to bottom. There can be big differences, 30 degrees cooler at the top (or at the bottom) of the kiln is no exception.

Many glazes clearly show a difference if they are fired higher or lower (see also this blog). PTCR measuring rings can be placed anywhere in the kiln, so you can measure temperature in many places.

Pyrometers do not measure accurately

It differs per type of pyrometer, but pyrometers are not always accurate, especially at high temperature.

In addition, pyrometers become less accurate due to wear and tear of the thermocouple (the part that is in the kiln). An old pyrometer can therefore indicate a different temperature over time than a shiny new one.

Grip on firing temperature = grip on end result

In short, if you want to get a better grip on the firing temperature, PTCR rings are an essential addition. More control over the firing process also means more control over the end result.

This certainly applies to glaze firing: some glazes are very sensitive to temperature differences. A firing temperature of 1250 or 1280 oC can make the difference between a beautifully melted or stone-matte (underfired) glaze. Or maybe even worse, if the temperature is too high, the glaze can drip off your pot and ruin your kiln shelves.

Can you only measure the heat work on ceramics with PTCR rings? No, certainly not. Seger cones have been in existence since the end of the 19th century. Today for sale as Orton Cones and they still work fine.

But these cones take up more space in your kiln. And you have to use a “pack” of 3 to 4 cones to check the firing temperature. But if you fire on gas or wood, the cones are still indispensable.

Are the PTCR rings a new development in the 21st century? No, the idea has been around for much longer and similar products have been developed by other companies. In England, the ceramics industry has been using Buller’s rings for a long time and in America the Orton TempChek are used.

And there are undoubtedly other products that I have not heard of (but what is not, can come).

The ceramic firing cycle

Process control is essential to my work. That is why I log the temperature of the pyrometer during the firing and check this afterwards with PTCR measuring rings.

If the temperature of these rings no longer matches the desired temperature, I will adjust that firing program the next time. Firing, checking, adjusting and looking forward to the next firing. The ceramic firing cycle.

Even if you are firing in another kiln or replacing an old kiln, the PTCR rings are your friend. With these rings, the mutual differences of the kilns are easily found and you can take measures.

I have a new kiln on order (exciting!) so I can soon get back to work getting everything under control in the new kiln (but that’s for another blog).

Don’t leave home without it

I love measuring, I don’t make a distinction: I love my pyrometer, Orton Cones and PTCR measuring rings equally.

My motto: Don’t leave home… uh I mean.. fire without them!

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About Post Author

Daniel Bende

Designs and creates under the trade name DFB-ceramics hand-thrown stoneware figurative ceramics.

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