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desert slip, from the horse's own mouth

updated sat 3 nov 01


Alisa og Claus Clausen on fri 2 nov 01

Dear Melinda,
Wish I was meeting you this weekend for the workshop. Instead I will be
home with my Rubber boots, standing flexible to keep standing, with very
strong winds we have lately.

Desert Slip. Urg. I understand that you want to continue to work with
this, as I wrote to Stephanie when I got it,
I am sick in love with it. It looks very good on dark clays and has a good
surface for the textured pots I am making now. It also has a nice melt
with a little cobalt in it.

But yours spits. I did a run of tests now to see if I could get it to spit.

All the following painted on bisqued tiles:
I mixed the Zircopax and Borax as poorly as possible, with chunks and
slapped it on with a big brush.
No oxides.

Same, but with ca. 5% rutile
Fired fast and flat. Showed brush marks.

Same, with Rutile and Ochre.
Same result, but slightly bubbly surface in areas.

Same with Rutile and RIO
Bubbly surface, but hard and fast.
I made one test with a lot of Ochre, do not know precent, but a healthy
amount in relation to base amount.
Surface also bubbled, but still hard and fast.

I added colored stains, at 10%.
Surface became dryer than usual.
Still hard and fast.

I added terracotta slip to the base slip.
Fired flat and fast.


I painted greenware with base slip.
Fired same as on bisqued ware.

Painted terracotta slip and desert slip mixture.
A lot of peeling.

Fired same test tile with just Desert slip over the peeled surface again.
Surface became fused.

But, there was no spitting in any of the tests.

So, what would that say to me. Non expert opinion, beware.
When I experienced spitting with all of my Colemanite tests in search for a
G.B. sub. in my glaze,
Tom Buck told me to sieve the Colomanite. It can be often contaminated
with gypsum. When I did this,
the spitting stopped, but many of the glazes were still too dull. My Frit
623 is a better sub.

I also scrape and dig ochre. Our local red clay has a lot of ochre in it also.

Could you try to sieve your materials and see if there is a difference. Do
one at a time to find out which, if any,
is the culprit.

I do not dissolve the Borax and as said, for these specific tests, mixed
the ingredients very rough. Still, did not experience spitting.

Also, I think it is important to correctly source glazes. The Frosty Glaze
was given to me from Tony Martens.
Also a glaze I use a lot. But very persnickety about making
crystals. Sometimes it is all clear, even with the same slower cool
down. Looks good over glazes, also the desert slip with ochre.

Let me know what happens,
best regards, Alisa

Have a great workshop.