Ovens and Oven Thermometers
I went to Wal-Mart and bought a neat fancy toaster oven with a timer on it. It fluctuated some, but I got a handle on it. It also died after about one year. I picked up a used toaster oven for $2 (yes, that's two dollars) at a yard sale back in 2001 and it is still steady in its temperature - something almost completely unheard of. If you are buying a toaster or convection oven, go cheap. You can buy six of the same brand, model and year and some or all will not hold a steady temperature. Don't know why, but quality control is a real hit and miss thing. I've known clayers to return ovens several times before getting one that holds true.
No matter what kind of oven you get - gas, electric, toaster, solar, wood, convection, etc. - is gonna spike and they vary from oven to oven, not just from brand to brand. You can buy three of the same kind of oven and all three will have different temperaments. In my opinion if you have the money, go for a convection oven - those are, I hear, more reasonably stable in temperature. You are gonna get some fluctuation from every oven, so get what you want. If you're going to do small items, a toaster oven is dandy. If you're going to do votives or larger items, go convection. If you're going to do really big items or multiple large items, go conventional kitchen stove.
GET AN OVEN THERMOMETER!! This is not an optional piece of equipment and having one has saved many a clayer from ruined work. Here's how it works. When you set your oven to cook at - say - 275°F (135°C), you get an average temperature of that. The oven will climb over that and spike, then shut off the elements and let the temperature drop to a predetermined level. Then it kicks the elements back on and climbs back up. So you need to calibrate your oven by placing a free standing thermometer in it and getting to know your oven's peculiarities. There are digital thermometers and the cheapie thermometers you find in American grocery stores. Both work well - the digital can be more sophisticated and, probably more accurate. I use a cheapie. Now, here's a neat trick: break up some red bricks, terra cotta, get some rocks, cement, stepping stones, kiln firing blocks - whatever's handy - and scatter them on the bottom of your stove. If you have two racks, place a stepping stone, ceramic tile or two or more, bricks, terra cotta pot dishes, on the lower rack. This will absorb the heat of the oven and give it back out, increasing the time between the temperature drop and spike. This also lowers your heat bill and, if you are using your oven for food as well, really cranks out some ideal meals. Okay, let's begin calibrating. First calibrate the thermometer. While at sea level the boiling point of water is 212°F (100°C). For every 500 foot increase in elevation the boiling point drops one degree. Thus, at a city 5000 feet above sea level, water boils at 202°F (94.4°C). For every 500 foot decrease (below sea level) the boiling point goes up one degree. So figure out what the boiling temperature for water is where you are. Bring a pot to boil, then place the thermometer into the water for five minutes. Pull it out with tongs and look at the temperature. If boiling temp is 212°F (100°C) and your thermometer reads 210°F (99°C), then you will subtract 2°F (1°C) degrees from what you see when you begin calibrating your oven.
To calibrate your oven, turn the dial to 275°F (135°C) or whatever the factory recommended temperature is on the package of your preferred clay. Place the thermometer on the oven rack where you plan to most frequently place your items, walk away and leave it for at least 30 minutes. This gives the oven time to spike, drop and respike - settling it down. Now pull up a chair and a good book because now you are going to get serious. Read the temperature on the thermometer. Do this every five minutes for an hour. *sigh* Boring. But very important. This will tell you how high your oven spikes and how low it drops. After that hour, adjust your dial either up or down taking your cue from where your oven spikes. You want your oven to stay below where your brand of clay will toast. I use Premo! and the temperatures recommended are between 265°F (129.4°C) to 275°F (135°C). I adjust my ovens so they spike just under 300°F (149°C) and then I marked my dial with a permanent ink pen on the spot where I really got the average temperature of 275°F (135°C).
Now - you're not done yet!!! Ovens have hot spots. On the same rack, the oven temperature between the rear left corner and rear right corner may very well be not only different from the prime spot, but different from one another as well!! And, if you ever consider using the lower rack, you need to know that, too!! So place the thermometer in a corner and come back in ten minutes. Read it and place it in another spot. Come back in ten minutes, read it and place it in another spot and so on and so on. When you've explored every possible location you think you will place items, then your calibration is complete. Now you won't need to calibrate again unless weird things start happening and your oven is going whacky.
Polymer Clay Projects
Online Jigsaw Puzzles of my polymer clay projects or
Online Jigsaw Puzzles of photographs I've taken in Oregon
Different desktop backgrounds.
Different craft offerings for your enjoyment. My way of saying thank you!
1) Coathanger Christmas Tree
2) Coathanger Wreath
3) Origami Giftbox
4) Tiny Hinges
Copyright 2004-2013 Colleen D. Bergeron.
Last revised: February 20 2013