My kiln has not been firing up well for the past few months. Since I was busy making and selling like mad all holiday season, there just wasn't time to look deeply into the problem. I continued to watch the time for each firing increase.
Things have finally slowed down these past couple weeks so I have assessed the situation with more care. The heating elements were all getting warm and turning orange. All the electrical connections seemed tight and without visible damage. The circuit box and power cord appeared sound. The kiln switch was blinking and sustaining the heat per usual. There was not an obvious solution to the problem.
I called my uncle. Not only has he been firing up kilns most of his life, but he's also an electrician by trade. He helped me replace my elements years ago when the kiln got wet, causing them to burn out. Although he is now completely out of the ceramic business, he has retained some of his equipment. He gave me his ammeter to use, a tool that tests the amperage going through the wires. I hooked it up in the fuse box and watched the dial expectantly. My kiln was not getting ample power.
I did some research on heating elements. Due to fumes in the glazes and clay bodies, firing to over 2200 degrees repeatedly builds up resistance in them. The ohms rating goes up and the kiln takes longer to get up to temperature. I took a chance and ordered a complete replacement set of elements. I removed the old ones, taking care not to damage the brick, and replaced each one - all by myself this time.
I fired up my kiln yesterday, keeping my fingers crossed. The deductions were right on. I am in shock with how quickly it finished - from 18 hours down to 6!
I have solved The Mystery of The Slow-Firing Kiln. The problem was simply ELEMENT-ary.