Crash cooling is also referred to as flash venting. Opening the lid of a kiln to cool faster from the processing temperature to the annealing temperature is known as crash cooling.
This process was originally done to avoid devit from forming on the glass. Manufacturers of fusing glass have all but eliminated this problem, by formulating fusing glass to discourage devitrification. And although we should give a lot of credit to these manufacturers for developing glass that is less prone to devit, there have also been advances in the manufactures of kilns that ensure the unit looses temperature quickly in the devit range. Manual cooling isn't necessary with Bullseye or Spectrum glass, but is still helpful with certain devit-prone glass.
What Are The Pros And Cons?First determine if the kiln is composed of fiber or brick. If the kiln is composed of fiber, then there are no worries for this process, except for the shock that it will give your kiln shelf.
Some individuals swear by crash cooling, while others say never flash cool a kiln. There are times when I flash vent and other times that I skip the process completely. This is mostly determined by the procedure I am trying to accomplish. Do the cons outweigh the pros in this process?
ProsManually venting a kin quickly can speed up the cooling process. Without opening the kiln lid and just permitting a piece to cool off naturally can be a very long process.
Venting will help to arrest a process, almost like freezing the desired look. It drops the temperature and keeps the fusing process form continuing.
There are a few procedures where crash cooling is necessary. For instance, when slumping glass through a drop ring, it might be necessary to flash vent the kiln to prevent the glass from slumping all the way to the kiln shelf or slumping further than desired. Allowing the kiln to cool on its own may not always stop the cooling process soon enough to control a drop ring slump.
ConsWhen opening the lid to speed the cooling at a top temperature isn’t shocking the glass. Flash venting at a high temperature is not hard on the glass. Crash venting is very hard on the fire bricks and elements inside the kiln. Similar to the damage that is done to a sidewalk from repeated freezing and thawing, flash venting puts wear, aggravation and stress on a kiln. Over time, the bricks in the lid of the kiln can crack, come loose, or start falling down particles onto projects. Some individuals still practice flash venting and have not had any degradation of the bricks. Turning the kiln elements off until the kiln reaches the targeted anneal soak temperature is much better for the kiln.
Crashing the kiln also runs the risk of stirring up powders inside the kiln and these could then be redistributed to the top surface of your glass. I have read that this dilemma can be eradicated or reduced with careful crashing.
Glass that is mixed with metal should never be flash vented. Because glass and metal have different rates of expansion and contraction, this will cause undue stress on the glass.
Crash cooling is also hard on your elements. Coils don't really like the quick change in temperature and if there are pins holding these coils in place, they can work loose.
As you can see, in general the cons do outweigh the pros. It is best to relying on your past fusing experiences, knowing the kiln's individual firing and cooling abilities and acknowledging all the dangers and hazards of crash cooling. Only you can decide what is best for your individual kiln and any future projects.