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two-piece vases.

updated tue 20 jan 04

 

Dave Finkelnburg on thu 15 jan 04


Pragati,
This is an excellent question!
There are many answers to it, also. In general, I like to join two
thrown pieces as soon as they are stiff enough to permit assembling them.
The softer the clay is when you join the pieces, the greater the chances
that the join will be successful and not crack.
Having said that, it is no problem to join pieces at leather hard. It
just requires techniques for that. Working at leather hard is exactly like
handbuilding where you are working with hard slabs. In both the hard slab
construction and joining wheel-thrown pieces at leather hard you need a
joining slip that is very thick, as thick as possible. And, you want to use
as little of that slip as is possible while still joining the two pieces and
excluding any air from the joint. At leather hard the pieces have already
shrunk some. Shrinkage of the joining slip will necessarily be great, so
the less of it there is, the less problem that causes. Also, covering the
pieces and the joint with plastic to allow time for moisture to equalize
across the joint is useful at leather hard. It is dry here, so I cover such
joints as tightly as possible with light plastic for 24 hours, then use
loose plastic or newspaper to allow controlled, draft-free drying after
that. Slather on lots of slip at the joining surfaces, then press the
pieces together as firmly as possible to squeeze out most of the slip from
the joint. You can scrape or sponge off any excess slip.
The kind of clay body you are using will influence what you can do.
Porcelain clay bodies are more difficult to join at leather hard than
stoneware bodies. It is especially helpful to keep the surfaces to be
joined damp. Seal the rim or foot to be joined with light plastic if
necessary to keep that part damp while the rest of the piece stifffens.
I've rushed through this, hope it makes sense to you. :-)
Dave Finkelnburg in Idaho, USA

----- Original Message -----
From: "Pragati Sawhney"
Sent: Thursday, January 15, 2004 11:46 AM
> Hi Everyone. I'm new to the group and have been an amateur potter for only
> about 3 yrs ... have a very basic question .. when you make two piece
vases
> ... or any thing tall in two pieces ... at what stage do you join the two
> pieces .. leather hard ?? or earlier than that ???

Pragati Sawhney on thu 15 jan 04


Hi Everyone. I'm new to the group and have been an amateur potter for only
about 3 yrs ... have a very basic question .. when you make two piece vases
... or any thing tall in two pieces ... at what stage do you join the two
pieces .. leather hard ?? or earlier than that ???
Thanks
Pragati

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John K Dellow on fri 16 jan 04


Pragati Sawhney ,
if you are going to put further shape in the piece then before leather=20
hard. The bottom section
needs to be just dry enough to take the weight of the second piece. This=20
will take some trial and error
to work out when . The type of clay is you are using comes into the=20
equation. Terra-cotta and be
a bit fussy . Too early then it may take the weight but split when water=20
is applied.

John

> . at what stage do you join the two
> pieces .. leather hard ?? or earlier than that ???
> Thanks
> Pragati
>
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John Dellow "the flower pot man"
From the land down under
Home Page http://www.welcome.to/jkdellow
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Michael McDowell on fri 16 jan 04


So far I've heard only advice regarding the joining of a two piece
vase at leather hard or softer stage. And with a thick slurry.
That's the way I've always done. But last year there was a display
of handmade high fired porcelain work, at COSTCO, no less, that had
come from China. It was accompanied with a video of the Chinese
potter doing joining to make some of these large vases. I was amazed
to see that the clay was very dry. It was so dry that they used a
sort of trimming tool to prepare one half to recieve the other. The
shavings came off like powder. Then they used a slip to join the
two. And yes I do mean a slip, not a slurry - very liquid. Has
anyone else seen this video and is anyone familiar with this
technique? It really didn't look like one of those car ads where
they use special effects and advise you not to try it at home. But I
wonder if there is some special ingredient in that slip and if the
porcelain they use in China has special properties that allow this.
I haven't worked in porcelain for a while, but that video intrigued
me.

Michael McDowell
Whatcom County, WA
Michael@McDowellPottery.com
http://www.McDowellPottery.com

william schran on fri 16 jan 04


Pragati wrote:>when you make two piece vases
... or any thing tall in two pieces ... at what stage do you join the two
pieces .. leather hard ?? or earlier than that ???<

As soon as the clay will allow you to join the two parts - meaning,
when the bottom can support the weight of the top without being
distorted. So, allow the bottom to stiffen but keep the area where
the attachment will be a bit wetter by covering with plastic.
Bill

Lee Love on fri 16 jan 04


A torch helps you join pieces more quickly, and even allows
you to keep the seams softer because you don't torch the edges that you
are going to join.


Lee in Mashiko http://mashiko.us

Web Log (click on recent date):
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marcia selsor on fri 16 jan 04


>Dear Pragati,
Like everything in clay..."it depends..."
I attach combo pieces at the slightly damper side of leather hard.
I have watched Spanish potters attach a previous thrown piece
(made in the am) to a freshly thrown piece made in the pm.
These would be for making large 2 feet wide x 2.5 feet tall
patio flower pots.
SO I think it would depend on ..
1. your clay
2. how dry you throw
3. how delicate the pieces are that you are attaching
Best wishes,
Marcia


Hi Everyone. I'm new to the group and have been an amateur potter for only
>about 3 yrs ... have a very basic question .. when you make two piece vases

>... or any thing tall in two pieces ... at what stage do you join the two
>pieces .. leather hard ?? or earlier than that ???
>Thanks
>Pragati
>
>_________________________________________________________________
>Check out the new MSN 9 Dial-up =97 fast & reliable Internet access with prime

>features! http://join.msn.com/?pgmarket=3Den-us&page=3Ddialup/home&ST=3D1
>
>______________________________________________________________________________

>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.

>
>

Tom Sawyer on fri 16 jan 04


No one much ever taught me but I am in the habit of throwing the bottom and
setting it aside to harden - then when I feel the bottom can support it, I
throw a thick ring which I place on top. The bottom of the top join is
widdened before placement on the harden under piece and I begin by throwing
down to seal the join; once I am comfortable with the join, I throw in a
normal fashion. This method is not much different from adding coils to a
hardened piece. The main thing is not to put to weighty of a top piece on
the bottom. While there is a difference in the top wetter piece and the
drier bottom, I dry slowly and end up with a nice smooth finish. I have
found this method works better for me than throwing both pieces at the same
time although this also works. I believe the wetter ring of clay that I
place on top gives me more flexibility as to the final shape. Probably many
wouldn't agree but heck I'm just an amateur.

Tom Sawyer
tsawyer@cfl.rr.com

Pragati Sawhney on fri 16 jan 04


Thanks to Dave and John,

I will try what you guys have suggested! I am using a stoneware clay body.
In fact ... Last evening .. before I got your postings .. I went home from
work .. and tried putting my pieces together ... and guess what ... the
bottom collapsed on me .. I think because it was still a little wet ... and
maybe the walls were too thin ... so that exercise was definitely a learning
experience :-) ! ha ha !! Will try another one this weekend.

I also thought it might be helpful if I kept the walls on the bottom part
relatively thicker ... so that it can support the weight of the top .. which
in my case was a long neck ... and since it was slightly more wet - probably
heavier.

Another Question ... I had an idea yesterday but have not tried it yet ...
maybe some one else has ... throw the bottom the regular way .. and for the
top... thrown a fat ring ... attach .. and then pull the top ... on the
bottom part ?? will that be easier ?? better ?? less cumbersome ???

Thanks again ...
Pragati

Gene and Dolita Dohrman on fri 16 jan 04


Finally, something I can contribute! Since I am fairly wimpy at centering
large chunks of clay, I have used this technique to throw a large piece.
Here is how I do it:
Center clay on a bat, throw a fairly thick walled cylinder (I like it at
about 3/4"). Open it all the way to the bat. I angle the flat part of the
rim outward.Take it off the wheel and sit it aside.
Center another ball of clay on a bat (or not, depending how good you are at
removing larger pieces from the wheel). Again throw it the same thickness
as the other piece. Do not open to the bottom, this will be the base of
your pot. I angle the rim of this piece inward.
Make sure the walls are the same thickness and the cylinders are the same
width (use calipers as this is important).
Score both rims.
Take the piece you have set aside and place it upside down on the rim of the
piece on the wheel. Before I use a wire to remove the bat from the top, I
use a small level on the bat to make sure I don't put to much pressure on
one side or the other. Use a cutting wire to carefully remove the bat. I
have had someone hold the bat in place while I pull the wire across.
Gently score around the seam where the two pieces meet. I usually take a
serrated rib and score over the outside and inside of the seam.
Now you are ready to throw the piece. Clean it up with a metal rib. At
this point I usually do a very gentle downward throwing from the top to just
below the seam. This compresses it somewhat. It is best to thin the top
portion of the pot first as you have already discovered, the base can
collapse under the weight. I have had really good luck this way and have
never had a piece crack or collapse.
Hope this helps. If you have any questions, just let me know.
Dolita

dohrman@insightbb.com
Louisville, KY

----- Original Message -----
From: Pragati Sawhney
Subject: Re: Two-piece vases.

Susan Giddings on fri 16 jan 04


It works for large bowl and platter shapes, too!


Usually I extrude large coils, but then I have an extruder handy and always set up. If you are not so lucky, you can just throw a ring in the way you have thought of. To start with I'd make just one and not too large - you can always add more. Don't know how much clay you are starting with for the bottom, but lets say just a 3 pound clay coil will work. Center it and open to the wheel head. Open as wide as the top of the bottom piece. Try to get about 1 " diameter ring of clay. A little larger than the circumference of the bottom piece it will be attached to.


It might be easier for you if you carved or pressed a shallow groove into the center of this ring.


If the bottom rim is still soft or you can make it moist easily enough, then just score it firmly but don't add slip - you really won't need to. The coil you just threw will be wet enough!


Take the coil you've just made, slice it from the wheel and cut it so that it is just one long band. Be sure it is long enough to fit the rim with at least an inch or two to spare. Starting carefully at one end, put the groove side down and nestle it well over the rim. (You'll quickly see that the groove is helpful even if not totally necessary. When you do things like this alone, two hands are limiting!) Squeeze and rock it gently and firmly so that it has sealed to the base piece without trapping air. Just work a few inches at a time until you get it all in place.


Where you have to join the two ends back together, lay the top most part over the bottom already sealed in place clay ring. You want a little bit of an overlap, maybe just an inch or two. (It's OK if it's longer. NOT OK if it's shorter!) Slice carefully through both at a 45 degree angle. You do this to join the maximum surface area and it makes this join stronger than if it was just butt at a 90 degree. Score the edges and slide and press firmly together trying to avoid trapping air. You should not need to add slip and certainly not water. Clay should want to join back to itself quite easily and quite well. Trapped air will be your enemy. Look out for it.


There are a lot of ways to smooth this into your bottom. At this point it's going to look like what it is - a big coil snake attached to the bottom. Once you do it enough you'll probably come up with your own way of smoothing it in.  I take a serrated rib and rub from the coil into the side wall trying to break both clay surfaces and meld the two clays together. Do this on outside and inside. Pay attention to NOT getting air trapped. I usually throw with ribs only at this point on, so I keep it all rather dry - soft yes, but no additional slip and surely never, ever plain water. I think someone suggested you use a torch, do it now to be sure the whole vase is firm and really set up. (Keep it moving slowly while you torch it though!) You will be amazed at how easy it is to throw with ribs, compressing the walls and thinning them. But go easy. Be sure it is set up. Otherwise something is apt to collapse. You might be better off to wrap it, let it sit and equalize everything overnight and make a new one while it's setting up!


I know that others will have tips for you on how to do this. Be prepared to practice! And please don't be discouraged. These are a lot of fun to make, always a challenge. Just take your time and you'll get it.


Hope this helps


S
------------------
Susan Giddings
Daytime phone: 860-687-4550
Cell phone: 860-930-8813



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Vince Pitelka on fri 16 jan 04


> In both the hard slab
> construction and joining wheel-thrown pieces at leather hard you need a
> joining slip that is very thick, as thick as possible. And, you want to
use
> as little of that slip as is possible while still joining the two pieces
and
> excluding any air from the joint.

Dave -
I regret the necessity of contradicting your generally wise counsel. Slip
implies a liquid medium. You are right in saying "as thick as possible,"
but that is a slurry, not a slip. Successful joining benefits from a thick
slurry. One should score thoroughly, with a tool that leaves shallow
grooves (like the Kemper serrated rib) and then apply LOTS of slurry.
Pressing the joint together extrudes all the excess slurry, which is easily
cleaned up. Advising "as little slip as possible" is unwise, since it can
allow a plane of bubbles to remain in the joint. The whole idea is to score
with shallow, wide groves (again, the Kemper serrated rib - never with a pin
tool or a wire brush tool that leave deep groves impenetrable to slurry),
and apply plenty of slurry, so that the joining pressure eliminates all
bubbles in the joint.
Best wishes -
- Vince

Vince Pitelka
Appalachian Center for Craft
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Office - wpitelka@tntech.edu
615/597-6801 x111, FAX 615/597-6803
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/

Culling on sat 17 jan 04


Has anyone mentioned weight? I only put 1/3 the weight onto the bottom and
if another peice is added 1/3 again.... Partly thrown and finished forming
after adding
- hope I describe this right - throw 2nd peice roughly (rough shape - not
refined and thinned down) upside down on a batt on a second wheel if
possible. When thrown do not cut off batt and make sure rims of both peices
are good and solid and well compressed and the same measurement!! , then
slip them both and take batt off wheelhead, tip upside down and place
slipped rims togther.( the batt is STILL ATTACHED at this stage!) you have
basicly got a ballon now made of a slighter stiffer than freshly thrown
bottom and a 1/3 weight roughly shaped fresh thrown top and the batt seals
the air insde - supports the form while you seal the two peices
together.Seal the join by throwing top rim down over botttom rim and when
firm brace batt on top agaist some part of your anatomy and cut off and
remove batt (I find I stand to do this for big peices) Then it's just a case
of sealing rims together on the inside of the form (yjrowning rim up) and
finishing the throwing, forming etc :-)))
Any queries??? Hope you can picture it!!bottom will always distort for me if
top is too heavy. Also not too sloppy throwing helps alot!!
good luck
Steph

>> in my case was a long neck ... and since it was slightly more wet -
probably
> heavier.
>
> Another Question ... I had an idea yesterday but have not tried it yet ...
> maybe some one else has ... throw the bottom the regular way .. and for
the
> top... thrown a fat ring ... attach .. and then pull the top ... on the
> bottom part ?? will that be easier ?? better ?? less cumbersome ???
>
> Thanks again ...
> Pragati
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
>

John K Dellow on sat 17 jan 04


Pragati ,
yes that is one way to do it.
Have a look at the demo section of my web page. I use vinager in the
joining slip.

>Another Question ... I had an idea yesterday but have not tried it yet ...
>maybe some one else has ... throw the bottom the regular way .. and for the
>top... thrown a fat ring ... attach .. and then pull the top ... on the
>bottom part ?? will that be easier ?? better ?? less cumbersome ???
>
>Thanks again ...
>Pragati
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
>
>
>

--

John Dellow "the flower pot man"
From the land down under
Home Page http://www.welcome.to/jkdellow
http://digitalfire.com/education/people/dellow/

ASHPOTS@AOL.COM on sat 17 jan 04


Hi all,, i make vases that i throw on 3 sections,, i then add 2 handles..

I throw a round form and i dont cut it from the bat .. later that day i
throw a neck and rim upside down.. I then cut the bottom with my cut off wire..I
flip the rim onto the round form and i use sponges in both hands and throw them
together.. NO SLIP, or SCORING..
I then cut the round form loose from the bat.. later when i feel the clay and
i can turn the piece upside down i trim the round form and throw a foot.. It
elavates the round form..I use soft clay and i then score and slip that part
and then keep throwing till i like the foot,, later when i can flip it again i
add my handles...

check out my website for examples: www.lookoutmountainpottery.com

Mark

Michael McDowell on sun 18 jan 04


Ivor,

You say "so long as there is some moiture". Can that be very little
moisture? In this video that I saw, the trimmings were coming off
like powder. While the pieces may not have been "bone dry", they
were certainly past what you would call "leather" or "hard-cheese"
hard.

Michael McDowell
Whatcom County, WA
Michael@McDowellPottery.com
http://www.McDowellPottery.com
...
Some years ago I had an article in "Pottery in Australia" which
dealt with the preparation of such a slip by deflocculation and
evaporative thickening to the consistency of "single cream". This
acts like "Superglue" provided there is some moisture in the clays
being joined.
Best regards,
Ivor Lewis. Redhill, South Australia

iandol on sun 18 jan 04


Dear Michael McDowell,

No, I have not seen that video, but you say <join the two. And yes I do mean a slip, not a slurry - very liquid.>> =
This I can believe.

What has not been made clear is that it is possible to get a smooth =
fluid slip which has a smaller proportion of water in its constitution =
than might be found in a seemingly thicker slurry. So there may be some =
confusion when comparing the opinions given from different sources.

Some years ago I had an article in "Pottery in Australia" which dealt =
with the preparation of such a slip by deflocculation and evaporative =
thickening to the consistency of "single cream". This acts like =
"Superglue" provided there is some moisture in the clays being joined.

Best regards,

Ivor Lewis. Redhill, South Australia

John K Dellow on sun 18 jan 04


Culling wrote:

>Has anyone mentioned weight?
>
I was taught to go 60/40%. That is 60% for the base and 40% for the top.

john

John Dellow "the flower pot man"
From the land down under
Home Page http://www.welcome.to/jkdellow
http://digitalfire.com/education/people/dellow/

Phil Smith on mon 19 jan 04


Folks,
When i make vase in two or more parts I usually continue to form the vessel
after the join. I form the bottom most area to near finished dimensions and
apply some heat to give it strength. Most of the water of plasticity is
driven off.
Area of join gets a very slight application of heat to set it a bit.
I use a tools known as "radius gages" to form a sort of tongue and groove
to get a near perfect match. I mix Epsom salts to solution and add the
thick slurry. Slight score and brush application of slurry.
The magnesium sulfate/slip solution will cause it to stick almost instantly.
There will be very little time for adjustment. 5 seconds or so.
If the form is to be a very large bottle type vase I normally add the neck
as a third piece to keep the weight of the second piece to a minimum.
If it is a little to stiff i'll reactivate a bit with slip,form the two
pieces to finished dimensions and reapply heat as needed to add the next
piece.

Phil...