Kurt Wild on mon 1 feb 99
I have sprayed glaze for years and often found small "goose bump" like
bubbles forming just about at the point when I feel I have reached a
satisfactory thickness. I know those "goose bumps" are small air
bubbles but am not sure why they form.
Any ideas?
They don't form when I dip pieces in the same glazes and no evidence of
the "goose bumps" remain after firing.
Kurt Wild
1000 E. Cascade Ave.
River Falls, WI 54022
Phone: 715-425-5715
email: kurt.l.wild@uwrf.edu
web site: http://wwwpp.uwrf.edu/~kw77/
Bill Aycock on mon 1 feb 99
Kurt- Is there a difference in the water content of the spray glaze and the
dip glaze ? I have heard that the cause of the "bumps" is-like this--
the clay is porous, and absorbs water, but- there was air in the pores
already- if the air water goes in, the air has to come out. The difference
between spray and dip situations may be the rate at which the water is
applied- slower with spray than with dip.
Repeat- - this is what I have been told-- I have not done the experiments
to check.- For instance- is there a difference that shows up when the
inside has already been glazed, compared to unglazed interiors? Is
thickness (of thepiece) a factor? If the piece interior HAS been glazed-
is the piece still damp?
to paraphrase another statement-- " Air gotta go somewhere!" so--- BUBBLES!!
At 09:46 AM 02/01/1999 EST, you wrote:
>----------------------------Original message----------------------------
>I have sprayed glaze for years and often found small "goose bump" like
>bubbles forming just about at the point when I feel I have reached a
>satisfactory thickness. I know those "goose bumps" are small air
>bubbles but am not sure why they form.
>
>Any ideas?
>
>They don't form when I dip pieces in the same glazes and no evidence of
>the "goose bumps" remain after firing.
>
>Kurt Wild
-
Bill Aycock --- Persimmon Hill
Woodville, Alabama, US 35776
(in the N.E. corner of the State)
W4BSG -- Grid EM64vr
baycock@HiWAAY.net
Mike Obrien on tue 2 feb 99
Sprayed goose bumps are caused by air coming through the glaze. It doesn't
happen usually until the third or fourth coat is sprayed on. The problem is
that the glaze doesn't have enough adhesion to resist the air pressure. The
solution is CMC gum or better yet Vee-Gum CER from R. T. Vanderbilt. I add 2
tablespoons to 96 oz. of glaze and mix for one hour on a bench-mounted drill
press. When its done I run it through an 80 mesh screen and its ready to go.
You can get either product from Laguna Clay.
Mike O'Brien
O'Brien Porcelain Co.
San Luis Obispo, CA
David Hewitt on wed 3 feb 99
Yes, I have also experience this. I spray several coats to obtain a
desired thickness. It seems to arise on the last coat when I have
reached the maximum saturation point. I have always assumed that the
body is unable to absorb the water fast enough and so forms a temporary
little 'goose bump'.
I have experienced similar effects when applying slip to leather hard
pots on both inside and outside surfaces. On the second side, which ever
this may be, I have at times found that this produces 'goose bumps' and
it if obvious to me that the clay is becoming saturated.
In either case I never found that this shows up when fired.
David
In message , Kurt Wild writes
>----------------------------Original message----------------------------
>I have sprayed glaze for years and often found small "goose bump" like
>bubbles forming just about at the point when I feel I have reached a
>satisfactory thickness. I know those "goose bumps" are small air
>bubbles but am not sure why they form.
>
>Any ideas?
>
>They don't form when I dip pieces in the same glazes and no evidence of
>the "goose bumps" remain after firing.
>
>Kurt Wild
>1000 E. Cascade Ave.
>River Falls, WI 54022
>Phone: 715-425-5715
>email: kurt.l.wild@uwrf.edu
>web site: http://wwwpp.uwrf.edu/~kw77/
>
--
David Hewitt
David Hewitt Pottery ,
7 Fairfield Road, Caerleon, Newport,
South Wales, NP6 1DQ, UK. Tel:- +44 (0) 1633 420647
FAX:- +44 (0) 870 1617274
Own Web site http://www.dhpot.demon.co.uk
IMC Web site http://digitalfire.com/education/people/hewitt.htm
C. A. Sanger on fri 5 feb 99
My experience has been that some glazes do not smooth out in firing.
Touch of Moon used in cone 10 reduction, sprayed thin, retains the
bumps. For the right piece, I like the effect, though the final piece
will catch dust and hold it like crazy. Have to run it through the
dishwasher to clean it. I've also noted slips don't smooth out, either,
but they can be burnished down if needed. Some glazes sprayed on thick
pile up like snowflakes. I always figured spraying glaze was like
creating artificial snow that had just enough water to stick to the pot,
but not flatten out. The intensity of the effect varies from sprayer to
sprayer. I've found those atomizer-type sprayers create the most
pronounced effect, and the size of the bumps varies more, looking sort
of like a faulty paint spray can that spits. I have no idea what role
air pressure plays, but think higher pressure might enhance the snow
effect. Maybe distance and angle affect it, too, since more "air time"
before contact could dry the globules some. Like everything else, you
just have to test your glazes so you know what they do before using them
on an important piece.
C. A. Sanger
Kansas, USA
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