Jump to content
Sign in to follow this  
dooarts

Darted Cups

Recommended Posts

I'm trying out making darted cups. I like them alot, but I'm having a problem with the rim of the cup distorting when it dries. I'm using porcelain, paper clay, and stoneware clay. They all seem to distort in basically the same way. I'm drying them slowly: 24 hrs wrapped completely in plastic, and then 12-14 hrs with a loose cover of plastic. Any suggestions from you clay veterans out there?

Share this post


Link to post
Share on other sites

try using strong paper cups inside the top when you finish the work.  just as you are about to put it away to dry, insert the right size cup and twist it until the rim goes round.  leave it in if the paper cup is sliding so it will slip upward when the cup becomes smaller.  it should just be resting on the clay rim, not stuck.

Share this post


Link to post
Share on other sites

The problem with the cups may already start with the making of the slabs. When you use porcelain your firing techniques also become important.  

Here are a few things to consider: 

 

How evenly spread is the moisture throughout the slab? 

Did you make sure the clay spread out in all directions evenly when you rolled it out? 

Do you carry the slabs in a way that it do not stretch? 

Do you make sure the slabs do not get dryer on one side than the other while you work with it? 

Do you dry the cups evenly, rather than slowly? 

What kind of drafts do you have in the room where you work as well as ( particularly for porcelain) in the kiln. 

Share this post


Link to post
Share on other sites

Where are you making your darts -- bottom of the cup, top, or middle? Could you add a picture?

 

When I am making round items (cups, vases) from slabs, I will take my slab, put it on a flat foam cushion, and roll it with a rolling pin to give it a curl. That gives the slab a curled/curved memory to revert to as it dries, rather than a flat memory. The clay in a slab cup tends to be more moist at the seam -- where you add slip, magic water, or spit to join the pieces; the join also tends to be thicker due to the overlap. So, it is important to dry slowly and let the moisture level even out. I prefer a long, tapered join on the seam to a short one.

 

I use both paper and Styrofoam cups to help keep the rim round while slowly drying. I cut out the bottom of the cup so that the walls give a bit to compensate for clay shrinkage when drying.

Share this post


Link to post
Share on other sites

You can actually throw an object on the wheel and alter it with darting. Slanted edges that overlap will prevent thick seems in the wall. One of the big mistakes that people make is to use slip. Good scoring and watering with vinegar in the water and scoring again is enough to let the clay create its own slip.  

Share this post


Link to post
Share on other sites

You can actually throw an object on the wheel and alter it with darting. Slanted edges that overlap will prevent thick seems in the wall. One of the big mistakes that people make is to use slip. Good scoring and watering with vinegar in the water and scoring again is enough to let the clay create its own slip.  

 

Steve teaches a workshop that part of covers darting thrown vessels that I highly recommend. Steve is a very talented. cool and fun guy. http://www.stevelouckspottery.com/

Share this post


Link to post
Share on other sites

If you're darting a thrown cup, take a page from Old Lady's book, and not only use the paper cup for drying, but use it while you're manipulating the clay while wet. You may be experiencing plastic memory issues. This is particularly true if you're experiencing the same problem with all 3 types of clay you mention using. It means it's something in the forming, not the drying.

Share this post


Link to post
Share on other sites

I've been making darted cups (handbuilt) and have had problems with the rims distorting, too. If you're darting at the bottom, Liz Zlot style, you've got a soft-square bottom and a round top - my rims tended to want to "follow the bottom" and go squarish. They also wanted to pooch out where the cylinder joined.  The tips above are excellent.

I do insert a cup of some sort with slanted sides - I have a big  plastic measuring cup that's perfect - to round the top. I tend to use it at intervals just to keep it from distorting while I work, or to round back up again when needed.

Be sure when forming the bottom to the squarish base to only square the bottom and keep the top round - it will remember.  

I bevel my cylinder seam at least 1/4 of the way in now so that it's not so thick, though if you're letting it show it loses depth that way. And after rounding with the cup I tap it in a bit there to compensate for the little bulge.

And I dry them really slowly, as advised above now - I always start them in a damp box, as my superstition is that that's the best trick for equalizing moisture. Then under plastic for a few days, and then a week or more in the air. 

I'm a beginner, too. I don't ask questions because so far I can *always* find my answer in a search of the archives here - it's an amazing resource and I'm so grateful for it and to all of you. 

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.