Fara Shimbo on fri 25 jan 02
Hi, all,
Does anyone know of any objective test or any standard way
to measure crazing? I'm trying to find a good way to compare
the crazing of my crystal glaze recipes to one another, and
on different types of bodies.
Fa
--
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Fara Shimbo, Certified Public Nuisance, Master Crystallier
Route 66 Ceramics, Hygiene, Colorado, USA
crystalline-ceramics.info ++ crystalglazes.info
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
"It's great to be known. It's even better to be known
as 'strange.'" -- Kaga Takeshi
Gavin Stairs on fri 25 jan 02
Hi Fara,
Here's a suggestion: Lay a straight edge or tape measure across the glaze,
and count the number of craze lines the edge crosses in a unit of distance,
say in one inch or 25mm. Try several measurements and take the
average. This will give you a measure of the density of the crazing
network. This is one variable.
Another is the relative shrinkage between the glaze and body. This you can
measure by dilatometry, or by making a warping tile: make a batch of thin
tiles of the body you are working with. Try to make the tiles as uniformly
thick as you can, and a couple of inches long. The thickness depends a bit
on the other parameters, so you may have to experiment to get good results
with your materials, but generally go as thin as you can without the tiles
warping very much in a bisque fire. Then glaze them on one side only, and
fire as you normally do. The tile will warp in such a way that the degree
of curvature is a measure of the relative shrinkage of the glaze and the
body. You will probably want to fire them in a test tile support, like an
IFB with slots cut to support the tile free of the kiln shelf. Like this:
(The picture will show up best if you view it in teletype mode, or with a
font like Courier.) The tile should not be glazed on the part in the
slot. If the glaze is runny, be prepared to sacrifice a slot for the test.
\tile ------>\_________\\ _________
ifb | \\\\ |
| | \\\\ |
->| slot------> \/ |
|______________________|
You can make this an objective measurement by measuring the sag over a
defined distance. You can use a depth gauge for this, or make one yourself.
gauge--> |<---- L---->|
\\|____________|//____|
tile---> \\____||____//______S
---------- |
The measurement is given by S/L. You can work out a true curvature number
from this if you wish. That curvature is a measure of the stress in the
tile as a result of the relative shrinkage of the tile body and glaze. To
be an accurate measure of the crazing potential of the glaze, you need to
keep the thicknesses of the tile and the glaze as constant as possible.
The more craze lines and the bigger the sag, the more crazy the glaze-body
combination.
Good luck with your experiments.
At 10:00 AM 25/01/2002 -0700, you wrote:
>Hi, all,
>
>Does anyone know of any objective test or any standard way
>to measure crazing? I'm trying to find a good way to compare
>the crazing of my crystal glaze recipes to one another, and
>on different types of bodies.
Gavin Stairs
Stairs Small Systems
525 Canterbury Road
London, Ontario
Canada N6G 2N5
telephone: (519) 434-8555.
email: stairs@stairs.on.ca
Attention!
On February 30, 2001 we moved to the above address from our
old address:
1A - 921 College Street
Toronto, Ontario, Canada M6H 1A1
phone: (416)530-0419 stairs@stairs.on.ca
Jim Tabor on sat 26 jan 02
Fara-
There have been some good suggestions to try. I was going to suggest a little
microscope like I have but wouldn't know where you could find it. There are
probably others like it. I bought mine from a German company (Seri-Plastica) at a
screenprinting trade show in 1983.
The view is ideal at 50x, has cross hairs with divisions at .002 mm that are
adjust to line up on the subject, and is lit from above at an angle. It is only
about 5 x 3 inches and sits on the subject to be viewed. Human hair measures .006
- .008 mm (3-4 marks). Glaze cracks you could not see without enlargement are
revealed and can be measured.
The macro view is the result of the micro. Besides the width and distance between
cracks, glaze bubbles, stain particles, color saturation, and surface qualities
are made more clear by a closer view. For instance, craters formed by granular
illmenite just look like specks in the glaze but under the microscope are
interesting as you can measure their size, focus on their rim and adjust the focus
down into the pit. I stopped using it for speckles in functional glazes after I
saw that.
It is pricey, but the Nikon Coolpix 950 can be attached to a microscope with a
range of views and provides pictures for future reference. I found it online when
I was shopping for attachments to the 950 I got for my girlfriend. I havent tried
the closest view of a glaze surface with her camera yet but at 300%, I could
clearely see my 15 year old daughter's skin pores, face fuzz, and other fine
details from a shot at 4 feet. Maybe a digital camera would give you all the
records you need for comparison.
The only other thought I have on the subject is to use a flat bed scanner to image
your crazing. Ive scanned areas of pots and other 3-D objects before and know you
will get fine detail you can enlarge on your computer to study and compare.
Good luck.
jt
> Hi, all,
>
> Does anyone know of any objective test or any standard way
> to measure crazing? I'm trying to find a good way to compare
> the crazing of my crystal glaze recipes to one another, and
> on different types of bodies.
>
> Fa
> --
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> Fara Shimbo, Certified Public Nuisance, Master Crystallier
> Route 66 Ceramics, Hygiene, Colorado, USA
> crystalline-ceramics.info ++ crystalglazes.info
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> "It's great to be known. It's even better to be known
> as 'strange.'" -- Kaga Takeshi
>
> ______________________________________________________________________________
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>
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iandol on sat 26 jan 02
Dear Fara Shimbo,
Are you asking about ways of making crazing show, or are you asking =
about how to determine the degree of deterioration of a glaze due to =
this defect?
I am working on a way of disclosing crazing,pinholing and other surface =
defects but the process will permanently stain the pieces.
Ivor Lewis. Redhill, South Australia
Janet Kaiser on sat 26 jan 02
Mask off or mark with a felt-tipped pen the area of a postage stamp or
similar. Count the number of whole areas between the fractures and make a
note. Then count those which are more than half and those which are less
than half. One "more" and one "less" equals one "whole". You then add that
number to the first you noted. Repeat on each glaze test.
Alternately you can count each more than half area as a "whole" and totally
discount each which is less than half.
That will give you an idea of the occurance of primary crazing. Needless to
say, secondary crazing (or crackling) can happen days, weeks or months
later, so you would have to go back and check again if that is important to
you.
You may need a magnifying glass and/or rub in some carbon or ink to help
definition for the count.
I am a little stuck for a word to describe the areas within the fractures
which are crazed. Is there such a word? Inter-fracture spaces sounds a bit
pompous, so I've stuck to "areas". I hope you know what I mean?
Janet Kaiser
The Chapel of Art . Capel Celfyddyd
Marine Crescent . Criccieth LL52 0EA . GB-Wales . UK
E-MAIL: postbox@the-coa.org.uk
WEB: http://www.the-coa.org.uk
TEL: (++44) 01766-523570
Home of The International Potters' Path
----- Original Message -----
> Does anyone know of any objective test or any standard way
> to measure crazing? I'm trying to find a good way to compare
> the crazing of my crystal glaze recipes to one another, and
> on different types of bodies.
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