Curtis Nelson on mon 19 mar 07
Mary Barringer's surface treatments have long intrigued me. Patient interplay of
slips, engobes and glazes on her slab-built pieces certainly has a special niche in
the ceramic world. If you're not familiar with her work, take a look at the April '01 CM
article on p. 47. Even better, look at and click on "artists" in
the menue to find Mary's name.
In taking some time to experiment with her recipes on p. 51 of the CM article, I
quickly found out just how unsure I am about slips and engobes as she's using them.
I was about to load my kiln for a ^6 glaze firing (all the pots have glaze liners) blithely
expecting the outside surfaces to mature also. Then, in the nick of time, I realized all
my various colored slip brushings, both before and after a ^08 bisque, were colors
added to a white slip base:
frit 3124 10
neph sy 15
ball clay 25
EPK 25
flint 25
To me, this recipe, with 50% of it clay, will never vitrify like an engobe (with much
less than 50% clay). Or isn't this recipe meant to be engobe-like? Or is it the frit's job
to give it engobe-like qualities in spite of the large clay amount?
So I'm not going to load the kiln just yet . . . too much good work to fire without some
confidence that this slip base will act like an engobe and not leave a dry and dusty
surface like I got after a ^08 bisque.
I suspect it will be the same after a ^6 firing. So, at this stage, what correction can I
make? Brushing on engobe-based colors can be done on top of everything, if that's
what's indicated.
How do I look at a slip or engobe recipe and determine if it's truly an engobe or just a
slip?
Is an engobe vitrious by definition? If so, why do people write and speak of vitrious
engobes? Isn't that redundant?
While I'm at it, there's some other recipes she offers I'm unsure of. One is called
"vitrious black slip." Now, to me, "vitrious slip" is just another way of saying "engobe."
Am I right?
vitrious black slip:
borax 10
neph sy 23
kaolin 22
ball clay 23
flint 22
add:
cobalt ox 1.0
copper ox 4.5
rio 4.5
In reading this, what is it that tells me that this is vitrious and not just a black slip?
Here's another recipe called "Stevenson vitrious engobe."
whiting 3.33
feldspar 8.88
frit 3124 50.00
ball clay 11.11
kaolin 13.34
flint 13.34
What do I look for in here to be assured that it's an engobe and will vitrify?
And one more.
Ash Engobe
talc 15
wood ash (unwashed) 20
cornwall stone 25
frit 3124 15
ball clay 25
Is it the less-than-50%-clay clue that tells me there's enough glaze materials to
insure vitrification?
Oh, is "glassy slip" really an engobe? If not, what in the world is it?
Gerstley 5
lithium carb 80
bentonite 15
Okay. Now I'm going to ask for some speculation. From what the article says as well
as my own workshop notes and pictures from three years ago in Asheboro, NC,
where Mary was one of three people giving demonstrations for a whole weekend. (I
wasn't experienced or knowledgeable enough back then even to ask good
questions or take notes on what I was seeing right in front of me and hearing what
was being said), Mary talked considerably about brushing on slips and engobes
both before and after bisquing. She may well have explained why, but I wasn't nearly
ready to "get" the significance and importance of when to do what or why. Fine.
Is there reason to use only slips or only engobes prior to bisque? Or can the layering
of slips and engobes be done without layering or pre/post bisque considerations?
That's enough. If this hasn't driven you crazy yet, it is doing that to me. Any clarity you
can lend will be so welcome.
Ready to be enlightened about slips and engobes,.
Curt Nelson
Asheville, NC, USA
There's plenty of room at the top.
It's the middle that's crowded.
Francis Whitiker
blacksmith
1908 - 1999
Colleen Riley on thu 22 mar 07
Hi Curt
I was hoping someone else would help you out with this one, but here's my
2cents...
I have been experimenting quite a bit with slips/engobes recently, so I can
relate to your confusion about what's what. I ^10 soda fire at ^10, but I
think some of what I've learned can be helpful to you:
>
white slip base:
>
>frit 3124 10
>neph sy 15
>ball clay 25
>EPK 25
>flint 25
>
First of all, it does look like this base might be dry by itself, judging by
the amount of clay vs. flux. With a 50% clay total, it will be a slip that
you might be able to get away with from leatherhard to bisque. But
definitely test it in your kiln. If the pots come out too dry you can refire
them with a frit or gerstley borate brushed over it to flux more. (My recent
favorite is wollastonite because it doesn't seem to craze as much...but not
sure if that would work at ^6).
>How do I look at a slip or engobe recipe and determine if it's truly an
engobe or just a slip?
Good luck finding a definitive answer on what exactly a vitreous engobe
needs to be! Every text seems to give a different answer. Your thought about
it being less than 50% clay is probably right, but it ultimately depends on
the silica/alumina/flux ratio. A vitreous slip does not have to look
'glassy' to be vitreous.
>
>While I'm at it, there's some other recipes she offers I'm unsure of. One
is called "vitrious black slip." Now, to me, "vitrious slip" is just another
way of saying "engobe."
I read somewhere that all slips are engobes, but not all engobes are slips.
I think (and glaze gurus feel free to chime in or correct me) that slips are
primarily clays or clay bodies, whereas engobes have other things added to
achieve particular qualities, such as vitrification.
>
>vitrious black slip:
>
>borax 10
>neph sy 23
>kaolin 22
>ball clay 23
>flint 22
>
>add:
>cobalt ox 1.0
>copper ox 4.5
>rio 4.5
>
This one is probably vitreous, but may not look glassy.
>
>Here's another recipe called "Stevenson vitrious engobe."
>
>whiting 3.33
>feldspar 8.88
>frit 3124 50.00
>ball clay 11.11
>kaolin 13.34
>flint 13.34
>
Wow, that one looks like it will be almost a glaze, with lots of
powerful-fluxing frit and only 24% clay. Might craze.
>And one more.
>
>Ash Engobe
>
>talc 15
>wood ash (unwashed) 20
>cornwall stone 25
>frit 3124 15
>ball clay 25
>
I read in an old text (Parmelee?) that Cornwall Stone is better than Custer
for vitrification. I am interested in trying this one...I'll let you know
how it comes out.
>
>Oh, is "glassy slip" really an engobe? If not, what in the world is it?
>
>Gerstley 5
>lithium carb 80
>bentonite 15
>
Yep, that one should be glassy. Looks almost like a wash to me. If my slips
(engobes) are dry, I'll add 5-10% lithium because it is a powerful flux, has
good color response and gives me nice reactive effects in the soda kiln.
>
>Is there reason to use only slips or only engobes prior to bisque? Or can
the layering of slips and engobes be done without layering or pre/post
bisque considerations?
It depends generally on the clay content and how thick you apply (not
whether it's called a slip or engobe). A slip with 80% clay likely will not
stick to bisque if applied thick, and an engobe with 20% clay will likely
not fit on a wet pot.
All of these recipes look interesting and should give you a variety of
effects. I'd try them all.
My final advice: experiment, experiment, experiment. There's a lot of leeway
with formulation and application, but you'll likely know it right away if
it's not going to stick. Borax (and gerstley borate? borate frits?)
supposedly helps with adhesion. (Vince, did you post that once?) You'll be
able to get away with more if you apply thinly or in multiple layers. A rule
of thumb is to put the highest clay slip on first, with others layered on top.
Good luck! Let us know how they look.
Ron Roy on thu 22 mar 07
Hi Curtis,
From what I understand about slips and engobes - this would be a vitreous
engobe - depending on how much stain you have added and if that stain is
refractory at cone 6 or one that helps melting.
I simply compared the Seger molecular formula of a cone 6 porcelain to the
formula for your slip. It is clear that there are more fluxes present in
your slip than in a typical cone 6 porcelain.
You can be sure there will be no dusting.
I cannot predict if there will be any fit problems however - you should
have tested for that before committing to a full load.
I don't have a lot of experience with engobes - well none that I can
remember - I have always thought that using the same body as a slip is the
safer way to go. This may not be appropriate for what you are trying to do
so you will have to simply do the appropriate testing to see if the new
coatings will match well enough on the clay you use.
RR
>Mary Barringer's surface treatments have long intrigued me. Patient
>interplay of
>slips, engobes and glazes on her slab-built pieces certainly has a special
>niche in
>the ceramic world. If you're not familiar with her work, take a look at
>the April '01 CM
>article on p. 47. Even better, look at and click on
>"artists" in
>the menue to find Mary's name.
>
>In taking some time to experiment with her recipes on p. 51 of the CM
>article, I
>quickly found out just how unsure I am about slips and engobes as she's
>using them.
>
>I was about to load my kiln for a ^6 glaze firing (all the pots have glaze
>liners) blithely
>expecting the outside surfaces to mature also. Then, in the nick of time,
>I realized all
>my various colored slip brushings, both before and after a ^08 bisque,
>were colors
>added to a white slip base:
>
>frit 3124 10
>neph sy 15
>ball clay 25
>EPK 25
>flint 25
>
>To me, this recipe, with 50% of it clay, will never vitrify like an engobe
>(with much
>less than 50% clay). Or isn't this recipe meant to be engobe-like? Or is
>it the frit's job
>to give it engobe-like qualities in spite of the large clay amount?
>
>So I'm not going to load the kiln just yet . . . too much good work to
>fire without some
>confidence that this slip base will act like an engobe and not leave a dry
>and dusty
>surface like I got after a ^08 bisque.
>
>I suspect it will be the same after a ^6 firing. So, at this stage, what
>correction can I
>make? Brushing on engobe-based colors can be done on top of everything, if
>that's
>what's indicated.
>
>How do I look at a slip or engobe recipe and determine if it's truly an
>engobe or just a
>slip?
>
>Is an engobe vitrious by definition? If so, why do people write and speak
>of vitrious
>engobes? Isn't that redundant?
>
>While I'm at it, there's some other recipes she offers I'm unsure of. One
>is called
>"vitrious black slip." Now, to me, "vitrious slip" is just another way of
>saying "engobe."
>Am I right?
>
>vitrious black slip:
>
>borax 10
>neph sy 23
>kaolin 22
>ball clay 23
>flint 22
>
>add:
>cobalt ox 1.0
>copper ox 4.5
>rio 4.5
>
>In reading this, what is it that tells me that this is vitrious and not
>just a black slip?
>
>Here's another recipe called "Stevenson vitrious engobe."
>
>whiting 3.33
>feldspar 8.88
>frit 3124 50.00
>ball clay 11.11
>kaolin 13.34
>flint 13.34
>
>What do I look for in here to be assured that it's an engobe and will vitrify?
>
>And one more.
>
>Ash Engobe
>
>talc 15
>wood ash (unwashed) 20
>cornwall stone 25
>frit 3124 15
>ball clay 25
>
>Is it the less-than-50%-clay clue that tells me there's enough glaze
>materials to
>insure vitrification?
>
>Oh, is "glassy slip" really an engobe? If not, what in the world is it?
>
>Gerstley 5
>lithium carb 80
>bentonite 15
>
>Okay. Now I'm going to ask for some speculation. From what the article
>says as well
>as my own workshop notes and pictures from three years ago in Asheboro, NC,
>where Mary was one of three people giving demonstrations for a whole
>weekend. (I
>wasn't experienced or knowledgeable enough back then even to ask good
>questions or take notes on what I was seeing right in front of me and
>hearing what
>was being said), Mary talked considerably about brushing on slips and engobes
>both before and after bisquing. She may well have explained why, but I
>wasn't nearly
>ready to "get" the significance and importance of when to do what or why. Fine.
>
>Is there reason to use only slips or only engobes prior to bisque? Or can
>the layering
>of slips and engobes be done without layering or pre/post bisque
>considerations?
>
>That's enough. If this hasn't driven you crazy yet, it is doing that to
>me. Any clarity you
>can lend will be so welcome.
>
>Ready to be enlightened about slips and engobes,.
>
>Curt Nelson
>Asheville, NC, USA
>
>There's plenty of room at the top.
>It's the middle that's crowded.
>
>Francis Whitiker
>blacksmith
>1908 - 1999
>
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Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
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