Do you know your oven?

Posted on March 21, 2025

I am not sure why I haven’t shared this on my blog before as these experiments date back some years!
As you may know, I used to work as a scientific researcher and had access to lots of cool tools and data loggers. I wanted to know what was happening to the temperature in my oven. I had been using those metal oven thermometers but I recognised that it was slow to respond as the temperature is indicated by the metal spring in the back that expands as it heats up. So it will tell you the temperature but it takes time to respond so it is showing you a sort of average temperature and doesn’t show you spikes.

I bought a thermocouple reader to give me an instant accurate temperature.

Using the thermocouple probe (or any digital probe thermometer) you could see the actual temperature in real-time and how it fluctuates – it does a lot! It was interesting to see how the temperature change in different places in the oven (cooler at the front as heat escapes through the glass door more easily). I then wanted to be able to show how the temperature changed so I ended up buying a temperature data logger – it records the temperature every second so you can plot a graph of the temperature over time. I was also looking to invest in some small ovens for polymer clay events at the time so wanted to make sure I got good ones.

Before I share the graphs a bit about ovens. Electric ovens have a thermostat that detects the temperature and turns the heating element on or off to try and maintain the temperature you have set on the dial. When the oven gets to your desired temperature it turns off the heating element, as it cools down and the thermostat detects the drop and it starts to heat again. This means the temperature in the oven is always cycling up and down. Your regular kitchen oven tends to have a larger capacity and better insulation than the small tabletop ovens which means the temperature variation is smaller and it will be less prone to spikes in temperature.

The build quality on small tabletop ovens is variable! They don’t tend to have very much insulation and they often don’t have very sophisticated thermostat control. They also aren’t very well calibrated so the temperature on the dial is often nonsense so please do make sure you always test this before curing your clay creations!

Here are some graphs from different ovens – the scales are all different so please bear that in mind when comparing them. Unfortunately, I don’t have most of the raw data now or I would replot them on the same scales to make them easier to compare.

Unbranded non convection oven

Here is a temperature graph from an unbranded tabletop oven without convection heating from turning it on for an hour. As you can see it took about 30 minutes to get to 150^o C (Kato Curing temperature) but in that time it was significantly hotter for at least 10 minutes. The temperature varied by +/- 10^oC even when it was at temperature. The temperature was wildly different from front to back too. This oven was offered to me by a friend to use for the workshop but I chose not to use it!

Branded (expensive) tabletop oven

I then bought a well-known branded tabletop oven with a convection feature to move the air around the oven thinking it would be much better. It cost £100 in 2015. I think I must have been trying to achieve 130^oC here. As you can see it was much the same running over 50^oC hotter at the start and then varying about +/-10 ^oC. The temperature around the oven was more consistent, a little cooler nearer the door. I returned that one.

Lidl Silvercrest convection oven

Then I managed to buy a Lidl Silvercrest small tabletop oven with a convection feature (there is a button on the front to turn convection on and off) It cost me £30 in 2015. Here’s what it looks like.

It still goes up above the called-for temperature when heating from cold (back to 150^oC for this one) but once it gets to temperature it is pretty stable at only +/-3^oC

I then wondered what would happen when I opened the door after preheating (as you need to do that to put your clay inside!). As you can see it took about 20 minutes to settle back down to a steady temperature and it did go a little hotter but not as crazy hot as when I initially heated the oven up. Not hot enough to cause problems for your creations.

So this is why I recommend Lidl Silvercrest ovens with convection feature – at least the ones from 2015!

Halogen oven

I know a lot of people like Halogen ovens – here is a temperature plot from a halogen oven – no initial spike and it got up to temperature more quickly than some of the other ovens but the variation is pretty high still at around +/- 8^oC . I prefer a door on the side for ease of getting things in and out.

Summary

What it taught me is that you should always preheat your oven, and a convection feature so the air is blown around and you don’t get hot spots is good. Putting some ceramic tiles in the bottom of your oven also helps to stabilise the temperature as they absorb and hold heat which helps to keep the temperature more stable, it will mean you lose less heat when you open the door for example.

At the end of the day, the main thing is that your creations are cured well enough that they don’t break and don’t get so hot they discolour/scorch/burn. If what you are making isn’t breaking/burning then what you are doing is probably fine! The average temperature you get from the round metallic dial thermometers is perhaps enough. The +/- 10^oC temperature variation shouldn’t cause a problem as long as your creations are in the oven long enough. But if you are a bit geeky (like me) you might be interested in the above graphs and it might help you understand your oven better.

If you want some more detailed information about curing polymer clay I would highly recommend the articles over at The Blue Bottle Tree