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Peepholes and Venting

Last week, we got an e-mail with a bunch of great questions about peepholes and venting your kiln when using powdered enamels dry on copper. So, we thought that we would give you some insights on venting for all kinds of enamels on glass, and metals too. Hopefully, this Q&A from Gail will help you in the future... it always helps me!  

Why does my kiln have a Peephole?
Large peepholes (viewports), tapered for a wide view without heat loss, were originally designed for manual kilns so you could see when the pyrometric cones bent. With venting as their secondary function, peepholes allow oxygen to be drawn into the kiln’s chamber and serve as an escape passage for metal oxides, smoke, and water vapor.

Do I need a Peephole Plug?
Peephole plugs are used to stop air from entering the kiln, not to prevent heat loss. But a kiln shouldn't be vacuum sealed, so It is beneficial to have some air entering the kiln at all times, It is not necessary that the plugs fit tightly.

What is the best shape for a Peephole Plug?
Peephole plugs are typically made of a lightweight ceramic material that can handle thermal stress well. Many plugs are interchangeable with different kilns, and the type of plug that is chosen is typically based on individual preference. The plugs with a tapered shape are designed to fit in just about any hole.
Should I leave the Peephole hole open or closed during firing? 

For plain old glass fusing and slumping, always fire the kiln with the plug in the hole as it helps the kiln reach temperature more easily. If you chose to leave the peephole out during firing to improve the oxygenation inside the kiln, be aware that this may cause a cold spot in the kiln.

  • When firing dry enamels on copper, leave the plug in the hole until you reach the top processing temperature, then remove it for proper oxygenation of colors as you insert your trivets and fork. When you are firing red, orange, or yellow enamels you should remove the plug so that more oxygen circulates in the firing chamber, keeping the colors bright. 
  • When firing liquid enamels on glass, leave the kiln vented or plug out until your reach 1000F. Then place the plug back in the hole. SOME (not all) liquid enamels need oxygen to develop to their juiciest potential!
  • If you want the kiln to cool faster, remove the plug. 
  • If you are doing a wax burnout, remove the plug. 
  • If you are doing a hollow core metal clay project, remove the plug.
          Are there fumes that come out of the Peephole that I should be careful of? 
          That depends on what brand of enamels... SAFETY FIRST! OLDER ENAMELS MAY CONTAIN LEAD THAT CAN BURN OFF IN THE TORCH OR KILN and will require proper ventilation of the area. Always do your research on enamels before you plan to use them.

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