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Bob Coyle

Member Since 06 Jun 2013
Offline Last Active Oct 08 2015 10:24 AM

#93909 Horse Hair Firing

Posted by Bob Coyle on 07 October 2015 - 07:29 PM

I have bisqued low fire clay and then used a propane torch to heat the pot to a temperature high enough to do a horse hair firing. If you pull the pot out of a low fire you need to let it cool down to the point where the horse hair will burn and leave a carbon trace. If it is too hot, the carbon will burn away. Too cool, and the hair wont burn to the surface of the pot.  There is a learning curve, not only on temperature, but also how you apply the horse hair. ( go to u-tube!!!)


As I said, I did horse hair fires with cold pots heated up with a propane torch. If the effect didn't look right, I just kept heating till the carbon trace burned off, and tried again. Horse hair firing is an art in itself. It ain't rocket science , but it isn't slam dunk either.


If you want to try it out of the kiln, then go for it. If you have a kiln controller, set it to where you see a low red heat. Pull the pot out, and when it loses the glow, start putting your hair on it till you get good traces. To erase mistakes, put it back in the kiln.

#91626 Can I Tumblestack Underglaze Greenware For The Bisque Fire?

Posted by Bob Coyle on 28 August 2015 - 06:50 PM

You SHOULD be able to bisque un-glazed greenware stacked. Under glazes is a different problem. If you fire below the flux temp of the under-glaze you probably OK. Err on the side of safety. and wipe the bottoms and don't stack them if you are not sure. Maybe stack one or two and try it.


If you are new to this, slow down and learn what will work and not work by testing non-critical pieces.

#90802 Making Pottery Or Metalsmithing

Posted by Bob Coyle on 13 August 2015 - 03:28 PM


whatever u guys do, do not mix glass and pottery

Yes, the COE is way off. the glass will crack if is fuses to the clay. I would still like to have a try at it with for a purely sculptural piece


In theory,  you might pull it off by creating a glazed ceramic piece as sort of a frame. The inside part of the frame would be left unglazed and have a undercut in the center


kind of like    {--------- glass -----------}  


The inside edge is then painted with non sticking kiln wash and dried. Seems like if you cut a thick piece of glass to just fit and then fired the whole thing at slump temperature the glass might flow into the frame and just form a mechanical fit rather than fuse. Then after annealing it and cooling it, you could clean off the kiln wash and the glass would stay in place.


As Stephen said though, you would definitely not want to do this where people might doing anything other than looking at it.

#90413 Home Made Kiln Controller

Posted by Bob Coyle on 07 August 2015 - 06:22 PM



The above is a link to the Arduino MAX31855 library . Why re-invent the wheel. I have been using the Arduino to control my kiln for several years.


Here is the code I use.


#include <MAX31855.h>

float tempOut = 0;
int command = 0;
int value;
// Adruino 1.0 pre-defines these variables
//int SCk = 13;
//int MISO = 12;//SO
//int SS = 11;//CS

// Setup the variables we are going to use.
double tempTC, tempCJC;
bool faultOpen, faultShortGND, faultShortVCC, x;
bool temp_unit = 0; // 0 = Celsius, 1 = Fahrenheit
MAX31855 temp(11, 12, 13);

void setup() {
  pinMode(2, OUTPUT);      // Test Com Reset issue  
  pinMode(3, OUTPUT);
  pinMode(9, OUTPUT);
  pinMode (10,OUTPUT);
  digitalWrite(10, HIGH);



void Average10() { // average 10 readings
  float Ave;
  int AveCt ;
  AveCt =0;
  Ave = 0;
  do {
      temp.readMAX31855(&tempTC, &tempCJC, &faultOpen, &faultShortGND, &faultShortVCC, temp_unit);
      Ave = Ave +  tempTC ; // tempTC ;
      AveCt = AveCt + 1;
     } while  (AveCt < 10 ) ;
    tempOut = (Ave/10);

void loop() {
   if ( analogRead(0)> 1021) {          // it's too high turn it off
     value = 0;
     if (Serial.available()) {      // Look for char in serial que and process if found
      command = Serial.read();
      if (command == 84 ) { // If command = "T" turn it on (unless to high)
         // delay (500); // keep it on for at least half a sec to prevent bounce
      if (command == 67) {          // If command = "C" turn it off
         // delay(500); // keep it off for at least half a second to prevent bounce
      if (command==68){                 //if command ="D" sound tone
      if (command==69){                 //if command ="E" end tone
          command = 0;                 // reset command
    Average10(); // take averaged sample
    Serial.print("@- ");
    Serial.print(tempOut);       // output to computer USB port
    Serial.println(" -Tmp ");


I use a Visual basic or a Java software  interface to do the logic to control the kiln. You can use any code that allows you to read/write from a usb device. 

A solid state relay is used to toggle the kiln on and off directly from the Arduino.


I use an AD595 chip rather then the MAX because Of noise problems. The AD595 is a very stable A/D for type K thermocouples. It works pretty much the same except you have to run it through a op amp.


Do some research on Google... there is a lot out there already done for you.



#90353 Making Pottery Or Metalsmithing

Posted by Bob Coyle on 06 August 2015 - 11:50 AM

I have been doing mixed media ( clay/metal/wood) pieces and they have gotten a good reception. People really like the the concept of blacksmithed metal bases on ceramic vessels.


I have really gotten big lately with an eight foot anthropomorphic clay and metal outdoor sculpture..


There are not a lot of people out there doing this type of thing, so it gives you a pretty good market nich, if you can combine both.

Attached Files

#89119 Stretching Your Limits

Posted by Bob Coyle on 18 July 2015 - 08:22 PM


I found that those had one continuous spiral crack running from 1" from the bottom all the way up to 1" from the rim. Like a spring! Hmmm. after lots of research, and talking to others including the folks at SC clay, I changed my firing schedule and had no problems.


Sometimes not all is a disaster, and a little help and research might help.

When I was doing engineering we "stressed to failure".  That was the ONLY reliable way to see how far a limit could be pushed in a real world situation. We pushed the limits till it failed... re-tweaked and tried again. Failure is absolutely essential... just as long as you are in a position to set things up so you learn from it... like Pres.

#87797 Clay Storage Environment

Posted by Bob Coyle on 26 June 2015 - 11:51 AM

I have had good luck with storing my clay in closed 20 gal plastic bins. I put a open container of water on the bottom and it keeps the clay from drying out through the plastic.

#74852 Firing A Sculpture With Aluminum Alloy Armature Wire Inside?

Posted by Bob Coyle on 04 February 2015 - 08:06 PM

if the wire is all connected together and is sticking out so that it is exposed to the atmosphere, you might be able to just melt it out and let it oxidixe without blowing anything apart.

Put a good layer of kiln wash on your shelves and bring it slowly up to around 1300F. This is above the melting point but below the boiling point. So all that should be happening is oxidation to the oxide , which is inert.

hold it ther for a couple of hours. Thin sheets or wires of aluminum oxidize quickly. That should melt/oxidize out the aluminum and give the clay enough strength to re- fire it after the aluminum has oxidized out.


It's worth a try.... any other way you will probably lose the sculpter.

#71021 Is There A Way To Distinguish Low-Fire From High-Fire Clay Piece?

Posted by Bob Coyle on 01 December 2014 - 11:56 AM


You could put the whole piece into a larger bisqued high fire bowl and then fire to cone 10 and when it melts its all contained in the bowl.
Thats the only way to avoid a disaster

Like Mark says...  Long ago I thought it would be neat to paint pictures on the surface of some commercial tiles I bought. They looked like high fire to me, besides I was just firing to cone 6... what could go wrong.


Well when I opened the kiln, there were no more tiles, only blobs firmly melted into the kiln shelf. Betcha I don't do that again.

  • Mug likes this

#70117 Input Would Be Great!

Posted by Bob Coyle on 17 November 2014 - 08:38 PM



I also like the look of Rebekah's forms. To me, this is how a beer stein/mug should look. I threw several similar forms for the prototypes I put out. Some people liked these (the more classic look) and some like the obvious " hand built" look which kind of surprised me. So I will do both for the up coming beer fest.


The manganese glaze/slip on the handle is one I poster here a while ago. I got a lot of comments that said it was not "food safe". which may be true, but I usually don't make stuff people eat  or drink from. I think it is fine for a handle though. I fire to cone 5-6 and I have made sculptures with this stuff that were copper plated for four days in a copper sulfate /sulfuric acid solution and the glaze  didn't look like it was effected so it won't come off in the dish washer.

below is the formula is you want to try it.


Ingredient                  Parts
Rutile                       27.00
Red iron oxide          26.00
Manganese dioxide   20.00
Ball clay                   10.00
Flint                           8.00
Frit 3134                    6.00
Copper carbonate       4.00

#68822 Tinkering With Commercial Glazes

Posted by Bob Coyle on 28 October 2014 - 06:11 PM

I never do anything other than brush glazes. I always use an polymeric brushing medium, rather than bentonite. The brushing medium, CMC or PEG or whatever forms a high polymer binder that literally sticks the glaze together on the surface of the pot, then burns off in the firing. I have never had trouble with flaking or any loss of glaze from the surface. I buy a ready made binder from the local clay store...probably mostly CMC... that has a mold inhibitor included. It costs more but is less of a hassle... no fermentation and stink.


The only problem I have with brushing, is that my students ALWAYS want to paint it on too thin. Once they learn to FLOW it on. the gazes look fine, and I don't need 5 gal pails of every glaze.

  • Mug likes this

#67899 Art Deco

Posted by Bob Coyle on 16 October 2014 - 10:02 AM

Yes Chilly, I think the word you are looking for is "Re-muddled". Sadly a lot of great old architecture was forever lost to a false idea of progress.

#67609 Setting An Electric Kiln Outside

Posted by Bob Coyle on 11 October 2014 - 01:36 PM

I had a old Kress kiln I kept outside and all I ever did was wrap it with tarps and attach bungees around it. The only problem I had was making sure it was wrapped tight around the bottom to keep the mice out. I used it that way for ten years,without a problem, until I moved.




You must live in some uptight community is it is not enough to allow a home owner to build to code... sounds like the contractors there have purchased the local politicians.

#65664 Making Cone Packs

Posted by Bob Coyle on 05 September 2014 - 06:38 PM

The lowest cone value should be first in the direction they lean. I always put the flat side toward the direction they will sag. I think this is the way recommended...pretty much like the picture. I never have used a protractor to measure angle. I just make sure that they are slightly bent towards the direction I want them to sag. if you wish to be more precise, that's fine. I like to fire my pieces to the point the middle cone ( the range you are looking for) touches down. Of course there should be three cones, one above and one below the cone you are shooting for. I leave just enough room for my cones not to hit each other when they sag. The lower ones should be pretty much down before the next one sags, so they can be within a cones width of each other. You want to be able to see them all through the peep hole.


Remember, firing a kiln load of ware is not something that can be absolutely reproduced from one firing to the other. As an old time potter I feel more comfortable seeing the middle cone down and the next higher just bent at the end of a run, but as has been mentioned many times, total heat work is what determines the glaze results on any run.

I have half a cone difference between the top and bottom of the kiln and it makes little difference for the glazes I use.


WRITE EVERYTHING DOWN! When a kiln load turns out right, try and reproduce conditions as much as you can and don't get to caught up in the some rigid set of "must do".

#64924 Review Of Steven Young Lee Show At Greenwich House, Nyc In Art In America

Posted by Bob Coyle on 22 August 2014 - 08:18 PM

Beautiful work. The "Vases with Eagles" makes an interesting counter point to the other pieces in the show.