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dipping in slip or glaze

updated tue 14 jan 03


Martin Howard on thu 9 jan 03

Much of my work is two tone slipware.
Light blue inside and dark blue outside.
I prefer the greens myself, but most visitors, especially the children at
the pottery parties, want their bowls in the blue.

Well that has always given me a problem of how to stop that bubble when you
dip the bowl upside down and are coming up to the rim, just as you get to
the rim the air pressure escape from inside causes an unwanted surge of slip
or glaze unevenly. All that work of using a levelling bubble to make sure
the line outside is level is spoilt by a wavy join inside

Over the last few months I have had a catheter because of my prostate
problems. The version before the "insert your own on demand" type that I am
now getting used to had valves. As I had to change the valve set each week I
collected these valves and now have quite a stock of them, thinking "they
will come in useful sometime":-)

I had used two for making a U bend of plastic tubing so that there was no
trapped air under the bowls. That is fine, if you want the slip or glaze to
read the same level inside as outside. But so often I just want the inside
RIM to be of the outside colour.

Had a dream last night! Use the valves actually as valves. Switch the valve
to shut for most of the deeper part of the dipping. The air pressure inside
means that the outside colour can only affect the inside rim. Then lift the
pot to rim level and open the valve to allow air pressure to equalise. Then
remove pot with everything level as required

In theory there should be no unwanted surge on the inside of the pots.
Now to put theory into practice.

Thanks dream potter for sending me that one!

Martin Howard
Webbs Cottage Pottery
Woolpits Road, Great Saling
01371 850 423
Updated 2nd January 2003

Martin Howard on mon 13 jan 03

Several have asked me offlist how the system I described for stopping that
bubble of slip or glaze actually worked.
It does work. Tried and tested.

You only need to remember whether you want the air flow open or closed.
I have slipped a lot of pots this way. All perfect!

Some were with the valve open, so the inside line is exactly the same as the

Others were first with the valve closed while the pot was dipped to the
level wanted.
(I am doing terra sigillata on the bottom of pots and marking the end of
that with two horizontal lines. The slip comes down/up to those lines. This
method gives me also lots of pot to hold when dipping slip or glaze.)

Then I start to take the pot out until there is resistance felt from the air
pressure inside.
Open the valve and continue taking the pot out of the slip.
Result is a perfect rim.

This just needs a little awareness of how the level of the slip and the
level of the open top of the tube adjust as you dip the inverted pot into
it. Too little tube showing and the slip level will rise and block the tube.
Too much and the tube top hits the top/bottom of the pot and creates a
vacuum when you wanted it to be a free flow air.

I certainly think this can be improved on by a little nick in the top of the
tube; a suitable clip to attach the outside tubing and valve to the bucket
so that nothing moves when one changes the valve setting, and a better way
of making the tube bend easily but stay in place. I have just used a metal
wire insert, which is really too strong. Minor things, but the method really
Oh, and always use a circular builder's level on top of the bottom of your
pots, so you really are dipping the pot level!

Patent? No just a gift to Clayarters!
Actually, I read of the basis of this method elsewhere, but with no mention
of a valve.

Martin Howard
Webbs Cottage Pottery
Woolpits Road, Great Saling
01371 850 423
Updated 2nd January 2003