On Second Thought...

As an afterthought regarding my last post, I'm thinking one of the main reasons I started this blog was to share with others how I do things as a way for us to help each other work through problems with our art. So I'll tell what I've read so far on how to do the simple, at-home test, for ceramic durability, suggested by other potters.

But 1st(to CMA) a small disclaimer:

Note: The following information is NOT instructions and should not be interpreted as such - I, in no way will be responsible for injury to anyone due to their following of my tips, ideas, steps, or any other information regarding the way that I performed, or will perform tests, or anything else, on my pottery or art. It is the responsibility of the reader/viewer/commenter of this information to use his/her own judgment, and do his/her own research on the testing of ceramics for durability, or performing any other procedure discussed on this site prior to doing his or her own testing.

Safety Tip: I would suggest wearing a long-sleeve shirt, hand mitten potholders, and safety glasses when performing these tests.

So far, I've performed the boiling/plunging test, whereby I:

1. Placed my liner test tiles in a zip-lock bag, placed them in the freezer for up to 24 hours (it's suggested to freeze for 24 hrs., but I don't think I froze my tiles every time for this long.


2. Then I carefully emptied them from the bag into a large pan (I used a dutch oven/a large sauce pan with handles on the sides) with just enough boiling water to cover the tiles. Moved them around with a spoon to make sure they were all covered in the water, then removed the pan the heating element on my cook-top (electric oven) and left the tiles alone to cool for a few minutes. I was attempting to simulate, as closely as possible, the action of one pouring a boiling liquid into a cup - once the liquid is in the cup, it would stop boiling and begin cooling.


3. I removed the tiles, using a slotted spoon, from the water and placed them on a towel to dry. After they were completely cooled, I checked each tile for crazing (small hairline cracks in the glaze which has a 'tiled' pattern to it), under a magnified light that I have in my studio. If your glaze is white like many of mine are, these cracks are sometimes very hard to see with the naked eye. See other ways for checking for craze lines below.
   


4. I repeated this freezing/plunging process 2 more times for a total of 3 times, which is suggested, and so far, none of the pieces have crazed. Now through my reading up on this, I understand that crazing can still take place, anywhere from a few days to months later. In other words, there's no guarantees when performing these types of 'home tests'.
   

TIPS- CHECKING FOR CRAZING:

Another way I discovered by accident to check for crazing is to dab some of the water from my 'throwing bucket' (stirred a little to kick up the silica from its bottom) onto the surface of a pot or tile. If the piece is crazed, the water will evaporate or seep into the cracks leaving the silica behind in the cracks, forming a pattern which is easy to see with the naked eye. Other potters' suggestions involve using water-soluble pens (use a color that will show up on your piece) to mark the surface which will show the crazed pattern, but I don't like the idea of messing up my test tiles using any kind of ink because I'm sure, even though it's water-soluble, once it's in the cracks, it would be hard to remove, as it is sunken into the clay body, which is exposed via these cracks. Another suggestion is to use a cheap microscope for viewing. Ron Roy suggested at a workshop that Radio Shack had (note, it's been several years since I attended that workshop) one at a reasonable price.

So that's how I did my first test for crazing. I'm sure it would have been better to perform this test using cups instead of tiles, but I just wanted to get an idea of how stable these glazes are before making larger batches of them and also, I didn't have enough cups to test and was anxious to go ahead and start testing.

I do however, plan to use cups for the second test, which involves heating in the oven, then 'quenching' in room temperature water. As you can see, this must be done with caution also, as anything can happen. Talk about thermal shock! What I've read so far (again, I'd suggest that you read up on this yourself, as I could be wrong in my interpretation of this information) involves placing the cup to be tested in the oven, beginning at 250 degrs. F. and 'progressing' up to 300 degrs. F. and staying at that temp. for 30 minutes. Here is where I'm not sure how fast one should raise the temp. From what I've read, it seems it should be done slowly, but how slowly? Let the oven come up to 300 degrs. F. at it's default rate? That would be pretty fast. This inquiring mind wants to know, if you do, please leave a comment, or let me know via e-mail!

Anyway, the cup(s) is heated at 300 degrs. F. for 30 minutes, then removed (I'll wear hand mittens and safety glasses for this test!) from the oven and placed into room temperature water (it's suggested to do this step in the sink for obvious safety reasons).

This is a harsh test and one that should be done with caution, as anything can happen, which I explained in my last post. I plan to try to use my studio sink for this, as it's a deep janitorial-type fiberglass sink. First, I'll place the dutch-oven I used for my test with the tiles in the bottom of this sink, fill it with enough water to cover the cup, and give it plenty of time to reach room temp. before heating the cup (I assume this is important, as too cold (yikes!) or too warm would not give an accurate result).

I've read (NOT from the ASTM site) that the ASTM says that a piece that passes this second test 3 times should be considered stable enough for 'normal' (to some, 'normal' may be what I or others would consider 'abnormal') use. As I mentioned in my last post, I never could find on ASTM's site where they explain this test and how to do it. It looked to me like they are wanting to charge a fee for their information, but maybe I was not doing a good enough search for the ASTM C 554-93 test. Now I have read enough to know that they are NOT talking about using these pots for 'flame ware' or on the cook-top. This is the industry-level stuff you see in department stores and even most of those ceramics are not made nor intended for cook-top or even oven use. I'm also, not particularly interested in making 'ovenproof' pots, as I understand one should use a stoneware clay which is specifically formulated for ovenware use. But I guess this second test would, if my pot passed the tests, make those pieces 'ovenproof' wouldn't it? I'm just not into making casseroles, etc. at this time, but who knows, I could certainly change course at any time! I'm just mainly interested in my functional ware being microwaveable (yet another test to be performed) and have a good 'clay/glaze fit', hence the thermal shock tests. Later...

Testing, Throwing, Painting

I've spent the past few days throwing a few cups in order to test my liner glazes. If you're interested in 'how' to test your funtional ware for stability, I would suggest going over to Clayart's potters.org forum or Masteringglazes.com for the detailed how-to's. I have completed the 'freezing/plunging in boiling water' method and so-far-so-good - no crazing!

A word of caution - Be careful when doing any type of 'shock' testing on your ware. Any number of things can happen i.e. popping, shivering (when sharp slivers of glazes literally fall off the clay-body), exploding, or whatever.

Because I consider myself a novice in ceramics, and most certainly a novice in the science of glazing, I don't think I should go into 'details' of how I tested. I would not want, in any way, to be responsible for someone's misinterpretation of my testing procedure (yeah, that's right, I'm chicken - Wuh Oh, this is sounding like the subject of my last post!). Instead, I would encourage anyone interested in the subject to go to the above sites. You can get enough info from the potters.org forum on how to test. And if you need more info, you can always join their listserve and ask for help. Ron Roy is a regular contributor to Clayart's listserve and I see John H.'s posts on there often also. A lot of times potters will specifically ask for Ron or John's help on a technical problem they're having. These 2 guys, as well as the entire listserve community are a sea of information. Have to admit, I quit subscribing to the listserve a few years ago, because I didn't like getting so many e-mails from them, even if only weekly. Once I got the e-mail I felt obligated, or just too curious, to run through it to see if there was anything I may be interested in - one more thing (like the WWW) to get side-tracked by. For me, it is much more convenient to go there for any particular subject I'm interested in. Saves time and uneccessary e-mails/reading. I go to that site for anything and everything concerning a problem/question I may have regarding ceramics.

Also, the potters there mention how the American Society for Testing and Materials ASTM (ASTM C 554-93) suggests testing for thermal shock, which will be my next step. I could not find on their site exactly where they explain the procedure on how to perform this test, but was able to pick up enough info in my Mastering Cone 6 book AND at potters.org to do the test; but I'll perform that test using cups, not test tiles. It involves heating the ware in the oven to a certain degree, then quenching in room temp. water, which is a more rigorous test than the first (again, be sure you research how to do this test before actually doing it and proceed with caution!).

And alas, on painting, just playing around with a mini watercolor (4.5" x 5") of a fallen oak leaf. I really want to get back to painting. Gotta make the time...

Now Where was I...

Oh yeah, when last posting, I was going down into the hollow to take some pics and assess the damage from the ice storm. Actually, it wasn't as bad as I first thought, given all the damage to people's yards and our streets. This is a pic of some trees on top of the slope that uprooted.
Surprisingly, many of the oaks that completely uprooted were fairly young trees, maybe because of their limited spread of roots. Some of the oldest trees took the storm much better. This image shows what a limited root system the young trees had compared to what a much older tree would have.

Many trees just split multiple times right down the middle of their trunks. This was especially true in town. Lawns look like they're landscaped with bouquets of 'toothpicks'.

Scenes of the bottom of the hollow:



Okay, enough pics of trees already! As I'm posting this, my husband is outside with the chainsaw cleaning up the mess and I need to go help. Back in a bit...

Cleaned up in the yard all day, now it's time to get back to art! I did accomplish one major goal over the past two weeks and that was getting my Etsy Shop set up. This is truly a milestone for me in goal-setting. Although I only have a few things listed so far, I feel that I can get things going now that I'm finally set up to sell on-line. Tomorrow I'll start testing my liner glaze tiles for durability. Will let you know how that goes.

The Glaze Fire

I'm very pleased with this glaze firing. The test tiles fired great. No visible signs of crazing or pinholes. I plan to test the tiles further for stability using Ron Roy and John Hesselberth's techniques. The following pics demonstrate how the kiln was loaded for this firing.

NOTE: The following points apply to any media I may be working in. I can see that I'll be repeating them often in the future! This info is intended for those of you who:

• are very new to ceramics who may not have the advantage of taking workshops or classes (hopefully you have taken at least a few classes in ceramics) and want to see examples of how someone else fires their pieces

• maybe you are familiar with ceramics but, like me, you enjoy seeing how other potters work, no matter what their (or your) level of experience. Each of us has our own way of doing things and this is just my way of working through/solving problems in 'the process' of creating. I'm a strong believer in 'there's always a better way'.

• have no experience with ceramics what-so-ever, but just enjoy reading blogs on the subject!

Top shelf was a 'half' shelf which held a bowl:

Next shelf, jars and some test tiles: I used 'wadding' to separate the lid from the glaze on the jar at left. Some still adhered to the glaze-where the heck is that dremel...

Third shelf ('empty' areas are where the posts were placed):

Bottom shelf:

As you can see, I have a teeny-tiny kiln. But I like it and it's all I could (and still can for the time being) afford at the time I bought it. Anyway, a larger one wouldn't fit my kiln room. I need to purchase about two or three more shelves and I'll be able to fire more jars and other items that don't take up too much space vertically.

Below are some pics of my test tiles. I held the firing for 30 mins. at 2185 (^5 temp.) degs. Far. which took my kiln (every kiln is different, so always use 'witness cones' to know exactly how high your firing actually went) to a little past ^6, almost to ^7 - maybe too far for the Ardvark clay, which is a ^5 clay. However, it didn't seem to hurt the glazes or clay at all. No blistering of glazes or slumping of the bisqueware.

Unloading the Kiln:

As I unload the kiln, I arrange the pieces on my kiln room shelves in the order they were in the kiln. This way, I can make note of where their location was in the kiln when I record the results in my notebook. In other words, pieces on the top shelf in the kiln correlate to how they're placed on my kiln room shelves, with the appropriate witness cone placed in front of each section. I write on the bottom of the witness cone with a fine-point sharpie, the kiln shelf location(e.g. top 'half-shelf';'2nd shelf'; 'third f/top', etc.). Now this is probably not necessary, unless my kiln were to fire very unevenly (which it seldom does) and affect the pieces' location in the kiln, but I do it anyway so I won't have regrets later:

Notice in above illus. the placement of witness cones for their particular shelf. See how pieces positioned behind the witness cone on the left almost went to a ^7 (the cone 7 is bent at about 11 o'clock. A bend to '9 O'clock' would have been a ^7 fire), while the witness cone shown on the far right in front of its pieces (bottom shelf location) the middle cone, cone 6, is only at 11 O'clock, meaning it only fired to a full ^5. However, I have to admit, I'm cheap and didn't want to waste using a witness pack that had a 'broken' cone 5 and 6 on it, so I think it actually went to a full cone 6. I'll try to remember to explain more about witness cones - what they are and how I make and use them in a later post.

Detail of test tiles:

Well, that's all for now. All of the glazes, or most of them are from Mastering Cone 6 Glazes, by Ron Roy and John Hesselberth. A good source if you're interested in ^6 firing. Later...

Blanket of Clouds

Well, it didn't get near as cold as the weather guys (and gals) said it would - only in the upper teens, thanks to 'low clouds' that moved in over night. So I'm glad for all the 'lil critters out there and people too, who have to brave the elements this time of year. Well, back to work, I'm preparing some more test tiles.

Cold, Cold, Cold...

Very cold and spittin' snow today. Supposed to get down to 4 deg. tonight; but I'm not complaining. I know people up north have got it a lot worse than us folks down here in Arkansas. Well, my goal for today is to decide which pieces I want to glaze for the next firing along with my cone 6 test tiles, and to prepare them by waxing the rims and bottoms. Til, then, stay warm...