Lili Krakowski on wed 27 apr 05
There is something that I do not grasp about long soakings to test glazes
for leaching.
I DO realize that a little dip in and out or just patting a lime slice onto
a glaze sample is not a test. I DO realize that the acid must do some work
on the glaze and that takes some time.
What I do no grasp is this:
When I go out in the sun for three hours I burn to a crisp. When I go out
in the 18 times for 10 minutes, I kind of tan. IS the acid test like that?
That the LONG exposure puts a more severe test on the glaze than the same
time broken up?
Or is it like the 32 machine washings some agency or something requires
before a garment can be listed as machine washable? That it would not
matter if the 32 washings are consecutive or interspersed--what they want is
32 times the half hour in the machine?
In other words that the 72 hour vinegar soak replicates 72 non-consecutive
hours with vinaigrette?
Lili Krakowski
Be of good courage
John Hesselberth on thu 28 apr 05
On Apr 27, 2005, at 10:48 AM, Lili Krakowski wrote:
> There is something that I do not grasp about long soakings to test
> glazes
> for leaching.
>
> In other words that the 72 hour vinegar soak replicates 72
> non-consecutive
> hours with vinaigrette?
Hi Lili,
There is nothing magic about a 3 day vinegar soak except that it is
easy to do and has proven by experience to be a good screening test.
Would 1 day be enough? Maybe. Would 10 minutes? Probably not. I haven't
researched it extensively and I doubt anyone else has either. But I
know if a glaze sample passes the 3-day test, the glaze will more than
likely hold up in use and leach minimal stuff in the lab test (which is
24 hours in room temperature 4% acetic acid).
Regards,
John
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
Ron Roy on sat 30 apr 05
Hi Lili,
I would not call it an extreme test - but you do need to test for what you
think may happen - worst case if you prefer that terminology.
The usual lab test for lead leaching for instance is 5% acetic vinegar -
room temp for 24 hours. Would that equal orange juice in a glazed pitcher
in the refrigerator for 3 days?
What about a tomato something in a casserole - cooked for two hours and
warmed up a couple of times.
Of course - some glazes come apart in much less time than all that - John
did a demo at NCECA - put some lemon slices on a couple of glazes and you
could see the shadow of those slices after only one hour.
What you are also looking for is long term degrading of a glaze - soaking
for 3 days and renewing the vinegar every day is a way of trying to see
what repeated exposure of a glaze to acidic food will do - over time.
When a glaze is etched by acid - the glaze becomes rough - attacked
unevenly by the acid. This process exposes more of the surface of the
glaze to the acid. So once the process is started it can go faster for
instance.
I makes sense to me - if you want to know how your ware will stand up over
time - develop tests that will tell you what you want to know.
RR
>There is something that I do not grasp about long soakings to test glazes
>for leaching.
>
>I DO realize that a little dip in and out or just patting a lime slice onto
>a glaze sample is not a test. I DO realize that the acid must do some work
>on the glaze and that takes some time.
>
>What I do no grasp is this:
>
>When I go out in the sun for three hours I burn to a crisp. When I go out
>in the 18 times for 10 minutes, I kind of tan. IS the acid test like that?
>That the LONG exposure puts a more severe test on the glaze than the same
>time broken up?
>
>Or is it like the 32 machine washings some agency or something requires
>before a garment can be listed as machine washable? That it would not
>matter if the 32 washings are consecutive or interspersed--what they want is
>32 times the half hour in the machine?
>
>In other words that the 72 hour vinegar soak replicates 72 non-consecutive
>hours with vinaigrette?
>
>
>
>Lili Krakowski
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Steve Slatin on sun 1 may 05
Lili, Ron --
Some thoughts on the lemon test/vinegar test.
Lemon juice has a ph of 2.4 -- vinegar is 2.8, orange
juice 3.0, but there are some foods that are much less
acidic. Tomato juice is 4.0. coffee is 5.0, and it
goes on from there. The PH scale is logarithmic --
orange juice at 3.0 is 10 times more acidic than
tomato juice at 4.0.
The beauty to using a good juicy lemon for the test is
that it gives you the most acidic attack that your
kitchenware is ever liable to come in contact with,
and the shape of a lemon wedge, with a curve and a
straight line both, will almost certainly be visible
if there's any change due to the acid contact.
Vinegar is good for the test, but the difference
between 2.4 and 2.8 is pretty big.
Ron's comments on the process of deterioration of
glaze surfaces expresses part of why it's not possible
to say that 10 hours at ph 3.0 is equal to one hour at
2.0 -- the surface quickly becomes irregular, and
likely less resistant to other attack. (Also, most
cleaning agents are alkaline, and there may be some
residual amount of the agent left when you first put
something into a recently cleaned dish/bowl/pitcher.
The alkaline attacks glass surfaces also, though the
chemistry of the process is naturally different.)
I knew a programmer once whose watchword was "there's
nothing like a live test." The lemon test is a great
live test. And it's cheap.
Best wishes -- Steve Slatin
--- Ron Roy wrote:
> Hi Lili,
>
> I would not call it an extreme test - but you do
> need to test for what you
> think may happen - worst case if you prefer that
> terminology.
>
> The usual lab test for lead leaching for instance is
> 5% acetic vinegar -
> room temp for 24 hours. Would that equal orange
> juice in a glazed pitcher
> in the refrigerator for 3 days?
Steve Slatin --
Sera que ela mexe o chocalho ou o chocalho e que mexe com ela
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