Marilyn T

Thanks for your reassuring answer Bill. ^6 self-supporting cone fired to 4 o'clock (optimum outcome was 5 o'clock). The total firing was 14:16. (Digitalfire was 14:20 so the total time was in line and the temps at the ramp changes also correlated). The only anomaly was the rate of 120 instead of 108 so I was a little concerned that the controller was not working properly, however if I don't get an error code then I'll assume it is within its acceptable speed range.

I programmed a C6DHSC program into my Skutt 1018 and the rates matched except in Ramp 3 which I programmed in for a rate of 108. The reading when I pushed the "5" key, which shows the programmed rate of rise per hour showed 120. I pushed the review button and it showed a rate of 108 in that segment. The 120 reading showed all the way from 2100 to 2200 and into the 10 minute hold. The rest of the rate readings are in line. This is the first firing since I changed the relays, elements and thermocouple. The previous ramp 2 had a rate of 350 (in my kiln 344). My amp reading reads 20 for both; This is not my normal firing schedule so I don't have a comparison from an old firing. My guess is that the kiln couldn't cool down from 344 to 108 quick enough but that doesn't explain why the rate didn't decrease over the 2100 - 2200 range. Any idea why this happened? Thanks.

Thanks for your reply Callie. I do like the clay but a defect free surface tops that. My current testing is to establish the best possible results for the Laguna 613 dinnerware set before committing to either refiring it to get a smooth white surface, or to glazing it with Rutile Green or Variegated Blue and using it in my own kitchen. I will add your suggestions to my list of firings as I continue to add to my knowledge base. With regard to the M390 glaze, I accidentally calcined the Ravenscrag instead of roasting it -- but from what I read it shouldn't affect the glaze -- it broke up fairly easily. Thanks for the heads up on the temporary change in texture of the M390. I did find it coarser than the Laguna 613 so hope it is smooth enough to allow rims to be unglazed -- if that is the chosen design. I purchased the box of M390 this month, so not sure if it is a minus 80 mesh sieve batch or not. I'll see what my absorbency tests reveal. Thanks again for generously sharing your ideas.

I have attempted to contact Laguna twice before about a different clay (Laguna 65) and received a reply that they were forwarding my question to someone else -- never heard back. So I probably won't contact them again. I recently purchased a box of M390 and threw some test bowls. I am including them in my next series of tests to see what the results are -- figured if Tony had success on M390 with the glaze G 3806 that I could use that as a comparison for the results on the Laguna 613 and go from there. He uses the C6DHSC firing schedule so if I don't have good results on the M390 it will indicate that something else is going on that I haven't thought about. As part of covering all the bases I'm bisquing a few bowls at ^02 for comparison. Going to give the Laguna clay about another 2 weeks to reveal its mysteries then abandon ship (I only have 6 bags left). -- 6 more glaze firings to go (the golf course is calling!) The good thing is that I am really good at throwing test bowls now.

Update # 2 for anyone following this thread: Results on Wollastonite Clear adapted glaze. Application: Varying the SG from 1.40 - 1.46 did not eliminate or make the problem better. I like the look of the lower SG and it has the added advantage of making it easier for the gases to escape. The addition of epsom salts to increase the thixotropy also didn't result in an improvement. Defect: more pinholes but smaller. (see photo 2X). I put India ink on the ware and viewed it through a jewellers loupe, because at first glance it didn't look too bad (no glasses; bad lighting) Causes of defect: (my theory) gases from body have not been fully expelled due to early melting of glaze which seals the surface (starts at 1800F); clay vitrifies >2150 before all the feldspars are expelled (2044-2192). oversupply of Calcium which has high surface tension (fluxes at 2012) and results in a glaze that is not fluid enough to fill the pinholes. Next steps: 1. try a glaze that has later melters and fluxes which lower surface tension. I will be trying the Studio White adapted recipe that Min sent me, as well as a similar recipe G3806 C and 3806 E from Digitalfire. They have lower B2O3 (0.10 to 0.15) and use Zinc oxide. (Zn limit 0. - 0.2 and the recipes call for 0.12 - 0.14 so shouldn't cause pinholes). All comments/suggestions/recipes welcome. Next update in a couple of weeks when I've finished testing the Studio white glaze.

Update for anyone following this thread: I have now finished my firing schedule experiments and didn't come up with a schedule that worked well. So far there are two possible solutions: (1) refire and (2) only glaze one side (to allow gases to escape from the unglazed side). I will use two firing schedules: my original firing schedule (the one that gave good results on Rutile Green, and Variegated Blue) and Min's suggested firing schedule which gave a good results for Studio White for the next set of experiments -- thickness of application and adjusted glaze chemistry. The results for the over 20+ firings are: peak temperature: the best results were in the range 2165-2190. I used both the 108 ramp and 27 degree ramp. Worse results were experienced going higher or lower than this range. soaks at peak: increasing the length of a hold from 2190: 5 - 30 minutes ; 2165: 18 to 30; and 2133: 30 to 75 didn't improve the results. slow cool rate: tried 500, 125 and 60 and got worse results the slower it went. The VB developed blisters with the extended hold. drop and hold soaks: soaks in the range 1900 to 2090 (going down by 10 degrees) didn't make any difference in the results for the Wollastonite Clear or Studio White. The only success on the VB and RG were in the original firing schedule. Next predicted update in one month.