Thursday, June 18, 2009

Element Design --- The End

I just thought I would try to end this thread by not going mathematical, but by speaking about the parameters that you need to be able to keep in mind when you are designing elements for a kiln. Anyone who is interested in how we did Papa Bear just let me know and I will do a separate post on that.

At any rate this will just be a review and crystallization of what we have done so far.

The most important variable is what is called watt loading, or the amount of watts per square inch that the elements have to generate to fire the kiln. Larger diameter wire allows for lower watt loading figures, but you have to be able to fit the wire into the kiln, and larger diameter wire also has less resistance per linear foot -- it's easier for the electrons to pass through a larger wire. So as you make the diameter of the wire larger, you need more of it to achieve the resistance that you need, and it may be so much wire that it won't be able to fit. We found that 12 gauge wire worked well for us, and that Kanthal A1 was the alloy that is the most economical and useful at the same time. Kanthal also makes an APM element but the raw wire cost is almost 5 times as much. It is special wire and I feel like it is not worth the extra cost as long as you have low watt loading. I think the watt loading for Papa Bear is around 12 watts per square inch. If we had decided to use 15 or 16 gauge wire, the APMs might have been a good choice, as they can go to a higher temperature.

We also have to take into consideration the diameter of the element. The diameter should be, according to Kanthal, about 5 to 6 times the diameter of the wire. Once we wind the element so that all the wire is touching we need to be able to pull the element to just over twice its wound length. The distance from the top of one wire to the top of the next wire is called the pitch and we want it to be just over 2 times the diameter of the wire. So we should be able to put a piece of element wire of the same size in between the stretched coils and move it back and forth a little.

We need to know how large our kiln is and how many kilowatts it will take to fire it. The Robert Fournier book has this information.

And we must keep in mind what happens when elements and banks of elements are wired in series and parallel.

Here is Galen Olmstead changing the element holders so that Papa Bear can accept the larger elements. We had to grind the element holders on the lap wheel so that we will be able to easily install the elements. Galen is beginning graduate school at UF this fall and he makes some wonderful sculptural objects.


Thursday, June 11, 2009

Element Design --- Answers to Questions -- Part 5

I was thinking that this thread has gotten out of hand by being so technical --- and no pictures --- which is why I shortened it but here are the answers to Dan and Alex's questions.

When I got Papa Bear I had discussed my needs with L&L and they sent this large 29 inch diameter kiln with 18 gauge elements, and the elements had almost no stretch to them. The kiln fired fine for a few firings and then it would not get to temperature quickly enough. I will mention that zinc crystalline glazes are quite caustic to elements and kilns so this was a new problem for them and that they have been really open to learning and overcoming the problems that we have. But anyway the kiln was underpowered and I just started using it for earthenware and bisque. It now will not even do that so something had to be done. The kiln was rated for less than 40 amps and that was not enough to make it useful.

I did not want to learn about element design because it hurts to try to keep all that stuff in memory at one time. But I have this kiln that is totally useless, and I wanted to bring it up to useful.

My smallest kiln, Baby Bear, has 137 firings on one set of elements so I know that there is a way to design elements so that they last a long time, but I don't know how to do it. I'll get a picture today of the elements of Baby Bear. There are twice as many element holders in Baby Bear as a normal kiln.

These new elements for Papa Bear, 12 gauge Kanthal A1 wrapped around a 3/8 inch mandrel and 8 ohms cost 72.00 each and the kiln needs 8 of them so a good part of this is wanting elements that last a long time. But it is also important for the kiln to be nimble -- able to reach temperatures quickly (both up and down) -- say at least 200F/hr at the end. Eventually this figure will not be able to be reached and we will have to replace the elements, but we want to be able to use them for as long as possible as 576.00 is 576.00.

By the way, if you have a newer Bartlett controller and you press 5 while the kiln is firing, it will tell you how fast you are going. Mini tidbit but impressive for onlookers.

It is true that my work requires more precision than most, but the principles apply to anyone who fires to cone 9 or 10 --- your elements will wear out at some point. Ray Gonzalez, who is the tech person at UF, says that kilns fired to cone 6 and below rarely need element changes.

One thing that is a good question is whether the kiln manufacturers should design their kilns for us. I say no, it is not their responsibility. They have to compete with one another and they have to make the best product that they can within those parameters, but they make "hobby kilns" and we have to adapt them to our purposes.

It's true that the L&Ls are made like a tank. If you stacked boxes of clay on top of an L&L stand, you would be able to go until the stack fell over. That stand could probably hold 500 pounds or more. Every other kiln that I have had has had a less robust stand, and I have had a few. Not that the stand does not still work, but I did get a feeling of confidence the first time I held an L&L stand.

Tonight I will go over the math stuff again but I am the cook today for the community and it basically takes all day to shop and cook. I cook every other Thursday. Yesterday was Anne's birthday and she requested black bean soup with amarillos and tostones and salad so that is what it is. Maybe a photo of the whole meal tonight if I can remember.


Wednesday, June 10, 2009

Element Design --- Our Final Idea --- Part 4

Well those elements are ordered and we now just have to wait for them to come. I sent the controller box down to Terry so he could install the Solid State Relays. These relays cycle on and off every 200 milliseconds so the elements do not get that much hotter than the kiln.

Here is what we decided to do. There are 8 elements in all in the kiln, three in each side section and two in the floor. We divided up the kiln into 4 sections of 2 elements each. This is quite different from how the kiln was originally wired, which was a 3, 3, 2 configuration.

Each of these pairs of elements will be wired in series within the pair, and all 4 pairs will be wired in parallel to each other. The elements will be 8 ohms each so each section will be have 16 ohms of resistance and 15 amps of current, and all 4 sections will generate 60 amps.

The wire is going to be 12 gauge Kanthal A1 wound around a 3/8 inch mandrel. This gives us a very good length to the element -- when it is stretched the pitch is just about perfect. And the watt loading figure is very low so these guys should last a long time.

Let me know if I need to be more specific about any of this -- how we did it, why we did particular things.......


Little Lemma Dilemma

Thank you Lee for the nice pun.

In my "Little Lemma" post near the bottom I mention about how my thinking had changed and now I have to admit, that was from right to wrong. I got out the Fournier book and saw that to get the distance it takes for a wire to wrap around a mandrel, you add 2 radiuses to the diameter of the mandrel, not two diameters, as I had. Sorry for this.

After thinking about it so many ways, and consulting my friend Terry Fallon, we have finally decided on the elements for the kiln.


Friday, June 5, 2009

Little Lemma

In one of my past lives, I worked towards a PhD in Mathematics, and could not resist throwing in a math term. Never did finish it but I have a Master's Thesis around here that is unintelligible to me now. Did I actually understand that?

A lemma is a small theorem which is used to prove a larger theorem. 

Suppose that we are going to wrap an 11 gauge wire around a 3/8 inch mandrel. How much wire do we need to go around once?

OK. What do we know? We know that 3/8 inch is .375 inches and that the wire diameter is .091 inches. We also know that the circumference of a circle C = πd where d is the diameter of the circle and π is 3.14. 

So what is this diameter? It has to take into account the diameter of the wire. It certainly looks to me like that diameter is .375 + .091 + .091= .557 and that the circumference is .557π = 1.75 inches. That is, it takes 1.75 inches of 11 gauge wire to wrap around a 3/8 inch rod one time. 

Here is my thinking. It has changed since I started writing this so I might be wrong. 1.75 inches is the circumference of the rod plus two wire diameters so it is the outside circumference of the wire wrapped around the rod. 

If we measure around the outside of the wire we get our answer. And anything less is not going to meet up.


Thursday, June 4, 2009

Element Design --- Wire Size and Pitch --- Part 3

This has been a very interesting time as I am trying to understand what makes a great element and, of course, get great elements in my kilns. The whole thing has been quite time consuming, but I feel like if I understand how to do this, I can maximize the life of my elements and the usability of my kilns. 

Here are my thoughts how to design elements for Papa Bear, which is a 29 inch diameter L and L kiln with 2 sections. There are 3 elements in each of the sections and 2 elements in the floor, so there are 8 elements in all. Since we want to have 60 amps, which will give us 14,400 watts, we divide the kiln into 3 different sections of 20 amps each. Each of these sections will be wired in parallel to each other. 

But within each section the elements will be wired in series. So the top section will have 3 elements wired in series, the bottom section will have 3 elements wired in series, and the bottom of the kiln will have 2 elements wired in series. That makes 8 elements in all. 

Let's look at the top section. We have 240 volts, we want 20 amps, so we need 12 ohms. (240/20 = 12) Since we have 3 elements in series each element needs to be 4 ohms. 

Now there are a lot of ways to get an element of 4 ohms depending on the diameter and type of wire, but I have decided that I am going to use either 11 gauge or 12 gauge Kanthal A1 wire. 11 gauge is thicker (.091 inches) than 12 gauge (.081 inches) and I would rather use 11 gauge than 12 gauge because it will last longer. 11 gauge wire also has less resistance than 12 gauge wire --- .106 ohms/foot as opposed to .134 ohms/foot. It's easier for the electrons to travel through a thick wire. 

However I have been told that 11 gauge wire is very difficult to work with because of the strength needed to wind the element, and also to install the wound element in the kiln. I don't have experience with this, but I do like the idea of using 11 gauge. 

Let's calculate the length of the wire needed for 4 ohms. 11 gauge is 4/.106 = 37.74 feet of wire and 12 gauge is 4/.134 = 29.85 feet of wire. 

Now we have to wind these wires on a mandrel and there are a couple of things we want to keep in mind, these courtesy of Kanthal.$file/1-A-5B-3%20UK%20resistance%20alloys.pdf?OpenElement

First of all we want the diameter of the element itself to be between 5 and 6 times the diameter of the element wire. This is so the heat can get out of the back of the element, and also so the element does not fall over when it is hot -- if the diameter is too big, the element won't be able to stand up when it is soft. 

Secondly, we would like to be able to stretch that element so that we have close to 1.25 element diameters between each pair of adjacent coils. We want to be able to take a piece of wire that the element is made of, insert it in the coils, and be able to wiggle it around a little. This is so the heat from the back of the element can make it out. Kanthal defines the "pitch" of the element to be the distance between the top of one coil and the top of the next coil and they specify that the pitch should be between 2 and 3. Our pitch above was 2.25. We don't want the elements to be stretched too much so we want to keep the pitch below 3 for an ideal element. 

When Papa Bear arrived the elements were of probably 17 or 18 gauge (They measure .040 inches) and the pitch was approaching zero. Just an unstretched element laying in the holders. I was only able to get a few cone 10 firings from them and now they will not even go to bisque. 

Next -- the winding of the elements. 

Thursday, May 28, 2009

S Type Thermocouples --- for Alex

If you look very carefully inside the photo of Baby Bear you will see the S Type thermocouple sticking out into the kiln. The S Type thermocouple is much smaller than the K Type thermocouple, but the thermocouple wires, which are Platinum/10% Rhodium and Platinum, are totally enclosed. The wires are protected from the atmosphere of the kiln. 

The thermocouple does not in any way come into contact with the elements. 

I believe they will last indefinitely if you do not break them. They are easy to break because they are small and delicate. I broke one of mine and my friend Terry Fallon fixed it. 

The caustic nature of the crystalline atmosphere does not touch anything but the porcelain sheath. 

I believe Omega is one company that makes them and Cleveland Electric is another. And most kiln manufacturers probably stock them too. 

Element Design --- Some Basic Kiln Parameters for Potters

There are a couple of features that crystalline potters should have with their kilns and I would like to look at these as a little digression from the calculations of the elements. I would say that every potter with an electric kiln should at least consider these features. 

The first has to do with thermocouples. A crystalline potter needs an S Type thermocouple. There are other even more expensive thermocouples, but we are discussing the difference between the K Type thermocouples that normally come on kilns, and the S Type that is an upgrade if you order it when you order the kiln. The S Type thermocouple has several advantages. It will measure temperature accurately through thousands of firings. It does not wear out. However you can not just retrofit your kiln with one of these babies because you need to change a chip in the Bartlett Controller ($10.00), and you need different lead wires. It's cost is around $150.00 compared to a K Type at around $25.00. 

However, Steve Lewicki of L and L Kilns recommends that you change the K Type thermocouple every time you change your elements. He says they are accurate for only a few firings and then they begin to drift. When I got my new L and L kilns, the thermocouples were protected from the atmosphere by a porcelain tube. After about 25 firings I took the thermocouple out of the tube and then tapped the tube on the table and there was a large pile of metal shards that had spalled off the thermocouple. No way that thermocouple was accurate.

So, bottom line is that S Type thermocouples cost way more when you get them, but they do not need replacement and they are accurate throughout their life. They are essential if you need to have any accuracy at all of your kiln's temperature. 

I must say that they are easy to break and you must be careful with them. I take mine out of the kiln when changing elements, something I learned by experience. 

Another thing that Kanthal recommends is using some kind of relay that is more sophisticated than just on and off. The idea is somewhat like that of a teenager driving a car with normal relays. The element is full on and then it is full off so it's like pressing the accelerator of a car full blast and then taking your foot off the gas full blast. This has the tendency to wear out the car, and it also has the tendency to wear out the element. 

My friend Terry Fallon is designing an incredible kiln and it has solid state relays. They cycle on for 200 milliseconds and then they are off for 200 milliseconds. This has the effect of not shocking the element and also of not making the element get much hotter than the kiln. These relays are more sensitive and they need to be mounted on a heat sink so they do not burn up, but Kanthal suggests that they will increase element life.

Wednesday, May 27, 2009

Element Design --- Resistance (Part 2)

So now we know that Papa Bear needs 67 amps, Mama Bear needs 55 amps, and Baby Bear needs 37.5 amps. From this we can calculate the resistance of the elements that we need to generate this many amps from the formula already mentioned, V = I x R. 

So, for 

Papa Bear,  240 = 67 x R and R = 3.58 Ohms
Mama Bear, 240 = 55 x R and R = 4.36 Ohms
Baby Bear,   240 = 37.5 x R and R = 6.4 Ohms

OK   let's just look at Papa Bear here for a minute. The resistance of 12 gauge Kanthal A1 wire is 0.134 Ohms/Foot so to get 3.58 Ohms we only need 3.58/.134 or 26.72 feet of wire. Hey that's a very elegant solution and it won't cost much either. Just 27 feet of wire and we can fire the kiln. But there is a major problem and we need to understand what it is and what we can do about it. Just because it works mathematically does not mean it will work in real life. 

Let's consider that our 27 feet of wire is a cylinder, where the diameter of cylinder is .081 inches -- that's the diameter of 12 gauge Kanthal A1 -- and the height is 27 feet. So we have a cylinder of diameter 81 thousandths of an inch and a height of 27 feet. The surface area of the cylinder is the circumference of the circle times the height of the cylinder. So we have .081 x 3.14 x 27 x 12 = 82.4 square inches of surface area. Note I had to multiply 27 times 12 so that everything is in inches. 

So we have 82.4 square inches of surface area and we need to generate 16,000 watts of power so that each square inch of element must generate 194.17 watts of power. (16000/82.4)

The online Kanthal manual 


would like for the watt loading figure of the elements to be around 15 instead of 194. That is, a good long lasting element will only have to generate around 15 watts per square inch of surface area. 

My guess is that our 27 foot element would last only milliseconds with a full 240V passing through it. 

Tuesday, May 26, 2009

Element Design --- The Three Bears (Part 1)

Here is a photo of my 3 electric kilns. They are all built by L and L and I have found the company wonderful to deal with, and open to learning the special needs of crystalline potters. 

I must confess that the kilns have names and they are Papa Bear, Mama Bear, and Baby Bear. It's kind of embarrassing to admit, but it does make identifying them much easier so the large one is Papa Bear, and so forth. Each kiln is 18 inches high and their diameters are 29, 24, and 18 inches respectively. The cubic footage of each of them is 6.7, 4.8,  and 2.7, also respectively.

So the first question we have to ask is, "How much power do we need to fire these kilns?" There is a wonderful book by Robert Fournier called "Electric Kiln Construction for Potters" and it is full of information like this. Actually he gives 2 different tables, "Power/Volume Relationship in British Commercial Kilns," and " Power/Volume Relationship in American Commercial Kilns." The British table suggests more kW (Kilowatts) than the American table, and since we want our elements to last, I decided to use the British Table. The British table allots each kiln almost half again as much power, and since I want to power my kilns so that the elements do not have to work so hard,  using the British table seems like the correct choice. 

Papa Bear, which is 6.7 cubic feet will require about 16kW, Mama Bear at 4.8 cubic feet will need 13kW, and Baby Bear, at 2.7 cubic feet gets 9kW. 

So now we need to know 2 simple formulas. 

The first is Watts = Volts x Amps or W = V x I where I is the current in Amperes, V is the voltage and W is the power to the kiln. 

The second is V = I x R where R is the resistance in Ohms. 

For my kilns the voltage is 240 so this will remain constant throughout the calculations. 


Papa Bear needs 16kW of power at 240 volts so 16,000/240 = 66.67 amps. We may not be able to supply that much because of the wire leading from the breaker to the kiln. But we will be able to improve on the 38 amps that the kiln was originally designed for, and which proved to be inadequate. 

Mama Bear needs  13kW of power at 240 volts so 13,000/240 = 54.16 amps.

Baby Bear needs 9 kW of power at 240 volts so 9000/240 = 37.5 amps.

Tonight I lead the chanting in our Temple and I have to sign off for the moment. 

But below is a photo of the inside of Baby Bear, and the double sets of elements. For some reason the hairpin turns offend my sense of craftsmanship --- I suppose it is the fact that the hairpin was not planned, someone just took the element and stretched it  ---- and I am going to try to eliminate the hairpins. 

Monday, May 25, 2009

Element Design for Electric Kilns

I'm in the process of designing new elements for my 3 electric kilns. 

For potters who do crystalline glazes, normal elements may last from 15 to 40 firings, and this means that we buy lots of elements, and that we spend lots of time changing them. But if an element is designed correctly, it will last for many more firings, and this was proven to me by redesigning the elements in my smallest kiln -- so far they have lasted 136 firings to cone 10-11. 

This redesign was the inspiration of my friend Jesse Hull. Steve Lewicki of L and L kilns actually did the calculations and made the new elements. It was a redesign of the whole kiln, as we now have twice the element wire as before, and it is much thicker -- gauge AWG 12 to be exact. 

The proper information to design elements is available online but it is much more complicated than at first glance. It's not as easy as it looks and you have to figure out basic parameters and then balance variables so that the elements work well. It would seem to be easy but it is not. However I am going to figure it out. 

This information is really essential if you do crystalline glazes but most helpful if you are anyone who wants to maximize the life of your elements. 

Before we get to the process of calculation -- and I admit that I do not have this all crystallized in my mind -- the most important variable is what is called watt loading. This is defined as how many watts per square inch of surface area do the elements have to generate. If they have to generate a lot of watts, they will not last as long. Bottom line. 

I wish it were this easy. Just design the kiln with thick elements and all is well. But it is much more complicated than that. Thicker elements have less resistance per foot, so we now have to have a longer wire to have the same resistance as before, and that longer wire may not fit in our kiln.

I am going to try to figure it all out and post it here. Dull subject but of great value. 

Monday, May 18, 2009

Gas Kiln Firing

Today we unstacked the gas kiln which I thought was going to be a disaster. The firing was fine even though it was too hot in the bottom and I struggled to get it even while keeping the atmosphere steady. The lower half was about a cone too hot. 

If you look very carefully you can see that there is a test tile which is very near to the left uppermost bowl. Too near as it turns out. I was able to remove it and do some work on the bowl, but it will always have a little mark. 

Somehow I expect my pots to be perfect. I'm not perfect and MY body certainly has 64 years of dings and doinks and I accept (mostly) these. I have a chiropractor and a personal trainer to help with balance, flexibility, and strength because I realize that I need to address these issues of imperfection before they become debilitating. Why can't a pot have a little ding and that be OK?

At cone 012 that same bowl was also holding up the cone but I was able to move the cone with a metal rod. 

There were some refired oilspot bowls in the kiln and this was the nicest of them, at least to my eye. The stoneware bowls are part of a dinnerware set for my friends Dean and Betty. 

I also managed to drop one of the peephole hard bricks on the Oxy Probe and it broke the porcelain tubing but did not otherwise hurt the probe. It will have to be fixed before using it again. This was the result of the leather gloves having a hole in the finger and me using a tea towel to remove the brick, the tea towel catching on fire, and me not being aware enough to figure out what is happening. 

I've been dropping stuff in the past week. Hopefully this is not the beginning of something permanent. I have to learn to be more aware. 

It's time to take the burners apart and make sure everything is working correctly. The fans seemed like they could use some oil. I have 21 year old Dedell forced air burners and they need some attention, especially since this is spring, and mud daubers love to build nests in small orifices. 

Friday, May 15, 2009

Detail Spray Guns

Well everyone, Ginny Conrow, ( uses a spray gun made by Iwata which lists for about 300.00 or so. I'm not sure of the price but it's expensive. I should have just gone out and bought one and forgotten about spray guns for life, but that would be too easy. Not my style.

So I went to Harbor Freight -- we have a new one in Gainesville -- and got a Central Pneumatic Professional HVLP Detail Spray Gun, Model 46719, for about 56.95. I used it and it was OK but I did not feel like it would keep me from wanting the Iwata. It's OK but not great and it seemed to get clogged by the glaze.

I went back there today because they have a very el cheapo spray gun, the Central Pneumatic Professional Mini Detail Spray Gun, Model 92126, for about 15.00.

It's not HVLP but I wanted to try it and when I got there it was on sale for 9.99. I got it home, hooked it up, and I just love it. It sprays smoothly and it resists clogging and it's easy to clean and it's kind of funky, but it really works well. Simple and direct.

So I will return the expensive one -- it's on sale now too -- and get a couple of the el cheapos and then --- well I still have to decide whether to get the Iwata. I mean it has to be better than some 9.99 knockoff, but how much better?

On another note, the gas kiln is stacked and firing. I had about 20 pots that did not make it which is disappointing.

Thursday, May 14, 2009

Stoneware Glaze Firing on Saturday

With any luck at all I will load the large gas kiln with stoneware tomorrow and fire on Saturday. Here is a group of mugs of which 8 will be included in the dinnerware set. Rather than making 8 or 10 mugs for a set, I like to make a whole bunch and not try to measure anything but the weight of the clay. That way there are some left over and I don't have to try to make sets, which I don't really like to do. 

In this next photo there are some of the dinner plates and some sugar jars with lids, and four vases in the background. There is also a bisque porcelain wiggle jar and a large porcelain covered jar which I have not decided how to glaze. The shelves at front right are filled with boxes of test tiles. 

Wednesday, May 13, 2009

Return to Thinking Out Loud.

Sorry it has been several months since I have felt inspired to write anything. That's not because nothing was happening, but I was just in a very private mood. 

Ginny Conrow ( and I led a crystalline workshop at the Dunedin Fine Arts Center at the end of February which was very well attended and we all had a blast. We started work at 8 am and did not finish until 10.30 pm each day. We had the use of some of the kilns of the local attendees and did altogether 6 firings, I think. 

I had a show at the Jacksonville International Airport for 3 months from January through April.

It's time now to get down to the day to day stuff of the shop. I am trying to finish a glaze load of stoneware to fire in the gas kiln. There is an 8 piece dinnerware set, some special order bowls, and I also have some oilspot items, which are being refired in reduction. 

Last year in August I came up to John Britt's in NC and attended his oilspot workshop and have been smitten by them ever since; not that I was not smitten before. Here is my best one so far. 

 They are not as easy to do as they look, that is, if they look easy. It's one thing to get a nice glaze on a test tile, and quite something else to make that glaze work on a pot. 

Saturday, January 10, 2009

Even more Bentone EW

I tried to get the batch of 300 grams of dry materials, 1 gram of Bentone EW, and about 4 tsp of CMC solution to work with 175 ml of purified water and it did not. The brush dragged on the pot. It's not that it was too thick -- it just did not work very well.

So I say that, for me, 200 ml of water is perfect for brushing this particular glaze on to this particular pot.

If you have a different glaze or clay, or bisque hotter or cooler, this will be slightly different for you but this is a good place to start.

Thursday, January 8, 2009

The Bentone EW story continues.

Yesterday I mixed a glaze with .33% Bentone EW and 200 ml of water. The exact specifics are 300 grams of glaze, 1 gram of Bentone EW, and 200 ml of water. I also added about 4 tsp of CMC solution. 

It worked really well for brushing; in fact it was a little watery so today I am going to try to reduce the water even more -- probably 175 ml. The less water there is, the more glaze there is in the water, and the faster coats build up on the pot.

I'm still pretty amazed by how little clay there is in the glaze, how well it brushes, and how well it stays in suspension. 

Friday, January 2, 2009

Ice Crystal

Today I made some ice in the freezer of the fridge in the pottery shop and came back to find this ice crystal sticking out of the ice tray. It seems very curious to me that something like this would happen. How could this crystal grow an inch out of the water? I did have the ice tray full of water and that might have done something with the surface tension of the water so that this thing would grow. 

Thursday, January 1, 2009

Specific Gravity for Crystalline Glazes and Bentone EW

Someone recently posted a question on the Crystal Forum about whether there is a perfect specific gravity for a crystalline glaze. My answer to that is that there might be, but I think this is not the best way to see the answer to the question, "What is the best, most efficient way to apply crystalline glaze to my pot?"

I think you have to take a look at all the variables, learn what part each of them plays, and go forward from there. 

The first thing to look at is how are you going to apply the glaze. The conditions are different if you are going to brush the glaze rather that spray or dip it. I brush all my glazes and so the specifics here are going to be about brushing. But the generalities apply to spraying and dipping too.

Next you have the glaze itself and most crystalline formulas have very little clay which means that they are not really going to act very well no matter what, if you don't do something. But you can do something and the glaze will be fantastic to use.

I have been working with a material called Bentone EW and it looks like it is going to be the only clay that I will need in my glazes, and it also looks like the glaze will be really nice with only .5% Bentone EW. Imagine a glaze with .5% clay which stays in suspension and brushes well. 

According to my friend Andreas Widhalm, Bentone EW is 10 times as powerful as regular bentonite. Bentone EW is what will suspend the ingredients in the water. It's much more powerful than Veegum T or Bentonite or Macaloid. 

I mix up glazes in increments of about 300 grams dry materials. To this mixture I added 1.5 grams (.5%) of Bentone EW, dry mixed with a fork,  and then added 240 ml of purified water and this made a very brushable glaze with the addition of some CMC solution. I think I can actually take out some of the water and have an even better glaze. Next time I will try 200 ml of water. I was able to brush the glaze on much faster than ever before. 

One of the major points is that the more water you have in the glaze, the longer it will take to brush it onto the pot at the appropriate thickness. So, if you are smart, you want as little water as possible so long as the glaze brushes wonderfully. 

Adding CMC will help the glaze to brush well. If you feel like your brush is dragging on the pot, you either need more CMC or more water. Again, according to Andreas, if you want CMC to thicken a glaze use it at a molecular weight of 300 or greater  --- CMC with a molecular weight of less than 300 will thin a glaze. You really need CMC for brushability. 

Finally for each different glaze you will need a measured amount of water, added CMC -- I make mine as a solution, and Bentone EW.

As an upper limit on the Bentone EW, I have a glaze with 2% EPK and 1.5% Bentone EW. I have added about 500 ml of water to get it to brushing consistency -- it also has a lot of CMC  -- and I can brush and brush and nothing happens much except that the pot gets wet. Almost no glaze material shows up on the pot. I applied about 20 coats this afternoon and only got about .005" of glaze and that is not enough. I will have to throw that glaze away as it is useless. Its consistency is actually thick so don't let thick or thin fool you in how much water is in the glaze. 

And I guess that's why I feel like specific gravity is not the right way to look at this problem. Specific gravity actually is used as a measure of solutions and a glaze is not a solution, it's powder hopefully suspended in water, which, I guess, makes it a compound. 

I hope this helps. I would encourage you to keep good notes on how much water you have in each glaze batch, and how well that batch worked for you in application.