Kiln Firing Basics

Firing Wet Ware? Preheat First

When firing work that hasn’t fully dried, using a preheat can help prevent cracking and other firing issues.

Kiln
Greenhouse
Bartlett
Tips & Tricks
By
Bartlett Instrument Team
on
August 27, 2017
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Using a Preheat for Wet Student Projects

With school starting back in full force, that often means its time to fire a kiln full of students' projects. Too often, the pieces are extremely wet, but it's time to move on to the next project. It's always good to dry your pieces as much as possible before firing to avoid issues. However, sometimes there's not always time to allow pieces to air dry thoroughly. This is where using a preheat with the kiln comes in handy!

Why Preheating Is Important

Preheating extremely wet pieces helps dry out the wet ware and helps prevent steam from cracking or exploding ware. Water turns to steam at approximately 212ºF, so it's important to preheat at a temperature lower than that. Typically firing between 180ºF and 200ºF is just right for drying out ware.

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How Long Should You Preheat?

Now you're probably wondering how long you should preheat for your particular project. These are some guidelines for preheating ware:

  • Pieces are thin and bone dry
    No preheat necessary
  • Pieces are thicker or slightly wet
    Approximately 4-hour preheat
  • Pieces are quite wet, thick or thin
    Approximately 8-hour preheat
  • Pieces are extremely wet, hand built
    Approximately 12-hour preheat
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When in Doubt, Preheat Longer

If you are worried about your pieces not drying enough, it won't hurt to program a slightly longer preheat. You can also check your ware towards the end of the preheat to determine if more time is needed.

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