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Member Since 26 Aug 2012
Offline Last Active Sep 30 2015 06:50 PM

Topics I've Started

Double Dip Flakes Off When Drying

01 August 2015 - 06:26 PM

A question for those who have the experience and knowledge….


A couple days ago I mixed up a batch of ‘Cobalt Blue’ for cone 10 and stoneware clay.  I have mixed and used this glaze before and never had problems.  However this time, when the glaze dries, it is extremely powdery.  It adheres well but I can easily brush off the drips while I would usually carefully shave the drips with a tool. My bigger problem is that when I dip the top edge of my cup in another glaze I usually use, the 2nd glaze cracks and easily falls off.  This double dip is a method I have used before and it worked beautifully with the glazes involved.  I also tried the 2nd dip using another glaze, with the same flaky  results, so I assume the problem is with my cobalt glaze.  I did fire a piece with the cobalt glaze only and the color and thickness showed no problems.

Here is the Cobalt Blue glaze recipe:

Custer feldspar             48.2

Flint                               24.1

Whiting                            7.7

Dolomite                          4.8

Gerstley Borate               4.8

Barium Carbonate           4.8

Zinc oxide – calcined       2.4

Tin Oxide                           .9

Copper                            1.9

Cobalt oxide                     2


Any educated guesses as to what I did wrong?  Can you suggest an easy fix or is recycle bin my easy fix? 

Thanks for all the help those of you share on this forum!


Oxygen Sensor/probe - Commercial Vs Homemade Auto Sensor

13 April 2015 - 10:36 AM

As I consider how I am going to 'improve my pottery' this year, I consider purchasing an oxygen sensor, however the price is a BIG consideration.  I fire an Olympic torchbearer, an updraft kiln, using LP to cone 10.  For the past 6 years I have used a sensor made from a Bosch auto sensor (Roger Graham directions).  It has allowed me to get reduction in my kiln but it is spotty and I feel I have little or no control over it.  I realize that weather conditions play a huge part in a successful firing and I am wondering if the cost of the new sensor will be justified thru better LP usage, more even reduction and more control over my (reduction) firings. Pottery is more than a hobby, but not a full time job, yet I do a couple shows a year and my pieces sell in a couple local stores - I see the payback as spread over a couple years. 


Input from those with knowledge and experience with oxy sensors will be appreciated.  I find only 2 on the market and cost ranges from $800-1200 so please give your best suggestions.




Making Plaster Molds

15 February 2015 - 10:45 PM

Hi All,

I have just finished making over 200# of plaster molds for our local Art Center and have come up with a few questions.  This is not my first time to make , but with the quantity I made, I seemed to have a variety of different ‘problems’.  I actually only ‘lost’ about 5 pieces of 50, so I feel quite successful as I do not work with plaster that often.  With your help, perhaps what I perceived as ‘problems’ will not repeat in future mold attempts.

For my molds I used new pottery plaster.

I weighed out my water and pottery plaster, as directed with my molds, to the ratio of.7 .

Plaster was sprinkled over the water and then left to slake for 2 minutes.  I then mixed gently from the bottom, getting rid of all lumps.  Then I let sit a couple minutes more, gently mixed, and poured it gently into silicone sprayed molds.  (Most of the time the plaster settled/slaked under the water but several times not all of the plaster settled so I had extra mixing – I did not notice any difference in my water temps or time – any ideas why it did not settle – plaster set up quickly).

I learned that water should be cool rather than warm or it sets too quickly.

Several times, altho the plaster was mixed well, as it set in the molds, a thin layer of water formed on top – what did I do wrong?  (I just laid a paper towel on the plaster to soak up the water.)

Also, twice the plaster did not even get warm -  why?  But it set up and appears OK.

I thumped my molds on the floor after filling to get rid of air bubbles but occasionally I had a few, very small, bubbles show up.  They don’t look large enough to cause surface problems in my clay – we’ll see.

I have been told to wait to fill the molds until you can draw a finger across the mixed plaster leaving a slight indentation in the mixed plaster surface – is that right?  At times it then seemed to set very quickly once I started to pour. 

I did learn that different brands of silicone release differently.

Molds have dried nicely by placing them in the area of our wood burner – can do a lot more at a time rather than in an oven!  However they do take about 4 days to dry.

Thanks for your comments!  They are always appreciated!  I learn so much from this forum!!

Oops - I Added Too Much Sodium Silicate To My Slip

28 October 2014 - 04:52 PM

Trying to mix some slip using slop and chunks from a recycling bucket and added too much sodium silicate - is there an easy way to thicken the slip up?  Right now it is like skim milk.


This is one of those times when I added more than intended and now I know why I should proceed slowly.

Firing Down

06 October 2014 - 07:04 PM

Temps are cooling here in MN and this Fall and maybe winter, I'd like to continue to fire my gas kiln.  I have an Olympic Torchbearer firing on LP and to Cone 10.  I can control a slow heating up when the kiln is cold in the AM but am wondering how, after reaching temp,  I go about slowing the cooling (and for how long) in a proper way so that glazes do not bubble from rapid cooling and pieces do not crack from shock.  My kiln is in an enclosed shed but the only heat there is from the kiln.  I don't want to damage my kiln or pottery just for a firing or 2 in the winter.  On a usual warm weather firing, I can unload the kiln about 36 hours after firing is completed.


I appreciate your sharing of knowledge.