venting for color and even firings

[martha peddicord]

I am debating putting a downdraft vent on my Skutt 1027.  I don't need it for health reasons, my kiln is under an outdoor shed roof.  I am hoping it will even out the cones from top to bottom, and improve colors.  Bottom is almost a cone cooler sometimes.  I always have at least 4" posts on the bottom shelf and 2" posts UNDER the bottom on the kiln floor.  I keep the bottom peep in and remove the 2nd and 5th peps.

Have any of you added a vent after firing your kiln without?  What did it change , or not have any effect.

[Nadine Mercader]

I added a vent system many years ago and found that my colors were better,  more vibrant.  I fire with an electronic controller and I put a separate pyrometer in the top also.  The top pyrometer is always 100 degrees hotter than the electonic display.  The biggest improvement for me is the environment,  my kiln is in the garage and I don't get any fumes with the vent.  My smaller kiln is unvented and you can really smell the difference,  especially in bisque fire.

[John Forstall]

If your kiln is in the open then you may want to think about all that shelf mass (weight) in the bottom to heat.  Its a surprise you only one cone cooler.

If you know your glazes, and with a good coat of kiln wash, you can use the bottom and eliminate the protection shelf.  If you still feel cautious about using the bottom make small slabs with fire clay to set pieces on.  Also the slower the firing the better distribution of heat work.  Soaking at the top may do as much, or more for your glazes than ventilation while also evening out the heat distribution. Worth a try  Good luck with that.

John255

 

[Norm Stuart]

I'm curious what your witness cones would indicate if you fired your kiln with just one peephole open.

Your 7 cu/ft kiln is twice as large as ours but puts out only 33% more wattage. We had an older kiln with this lower heat to volume ratio which fired unevenly, according to our witness cones.

Someone mistakenly fired our new kiln with both peepholes open (we have only two) and the bottom of our kiln was well more than one cone cooler and the top shelf was too hot. Our one thermocouple is in the middle of the kiln.

For better or worse we place three 3/8" thick pancakes under the bottom shelf. This places the side of the bottom shelf directly in front of the bottom row of elements (each 4.5" tall layer of firebrick contains two rows of elements). This arrangement provided us with even witness cones placed on the bottom, middle and top shelves. Far better than laying the bottom shelf directly on the firebrick floor.

Being outdoors we don't have an exhaust fan on the kiln. This means I can deliberately lightly pink a tin white majolica by placing a chrome glazed pot on the same shelf, but with the chrome glazed piece placed higher in elevation than the white majolica to be pinked. So obviously we need to load the kiln with this cross-contamination in mind when it's not desirable.

The pink color of cross-contamination on tin white majolica, from a chrome glazed pot placed on a half-shelf above the plate.