Joining Clay With Slip

[Melissa M.]

I am just learning to join clay pieces. I recently made a piece with stoneware clay. I scored the surface of both pieces (both in the wet stage), applied slip to the main piece, and gently pressed the joining piece onto it.

 

When it dried, it seemed to be joined well, so I started to apply the underglaze. Near the end of underglazing, I accidentally applied a little pressure to the piece, and it broke off.  

 

I have a few questions:

 

- Any idea what I may have done wrong?

- Is there any way to test the join of clay pieces in the wet stage? How about in the greenware stage?

- I know that greenware is super fragile. Is it possible that this is normal, and I just need to be very gentle with the piece?

- Once it breaks in the greenware stage, is it easier to recycle it than to try to repair it?

 

Any other advice regarding joining clay pieces would be great! 

 

Thanks,

Melissa

[MMB]

Add a bit of paper pulp to your slip. Use a standard basic toilet paper or if you have easy access to cotton linter. That will aid in a strong bond and aid in stonger green ware and then on. Im having a hard time understanding how it broke. If you scored properly and added slip then it should of been firm. Maybe your slip is too watery and there isnt enough clay content. Maybe your scores were too simple and maybe just simple drag lines.

 

Dont recycle the pieces now. Get yourself some paper clay slip and rebuild then clean up.

[Marcia Selsor]

Could be too much underglaze moisture soften the area of the joint? Very hard to say. I agree with MMB. Mix up a little batch of paper clay paste and put it back together.

touch up the underglaze.

 

Here is where I got the original spooze recipe. I have added paper pulp, about 20% of the dry clay in quantity.

Peggy Herr was an early clay art participant. She developed this recipe. She died in 2006.I add paper pulp to this.about 20% to the clay portion.

This is her recipe.

 

 

1/3 parts dry clay powdered....any body...preferably the one you are using 

with no grog 

1/3 parts heavy karo syrup 

1/3 parts white distilled vinegar 

 

 

A drop of hydrogen peroxide to keep it from spoiling...it will bubble for a 

few minutes and then settle down. if you dont add that the sugar goes bad 

and smells awful in about a day. 

Marcia

[bciskepottery]

Even well scored and joined pieces can break if subjected to stress.  For you slip, you have a variety of options:  your clay body and water; your clay, water, and a bit of vinegar; water alone; vinegar alone; magic water; saliva (yep, the old-fashioned way); commercial concoctions.  But, any joint will be subject to stress regardless of how/what was used.  It could be you need a reinforcing coil behind the join . . . a picture of the piece would be helpful in better understanding what happened.  Goods joins are a result of learning from mistakes, we all make them; eventually, you'll find what works best for you, your clay body, and your forms. 

[GEP]

You said you "gently pressed" the pieces together, but a strong connection requires pressure. Next time, firmly press the pieces together. There are ways to do it without marring the surfaces with fingerprints, it takes strategy and practice.

[perkolator]

I would guess your scoring marks were not deep enough and you didn't push the two sides together hard enough. I'm a fan of using the same clay body as joining slip mixed to about yogurt consistency, I use a plastic fork to score because it yields a little bit under my hand pressure vs metal fork. score marks usually aren't so deep they make air pockets, but deep enough to give good bite. lastly I always use a sharpened chop stick to "stitch" my seam by moving material from one side to the other being careful not to integrate air bubbles at the joint. With a method like that and possibly reinforcing joints with a coil of clay, you will have fairly bulletproof connections. If the clay is more toward leather hard, adding vinegar or magic water will help the bond chemically speaking - on soft clay this is unnecessary because its soft enough to move around but can still be used.

 

The whole idea is to make the two pieces of clay become one piece or they will likely fail at the joint. Interlace your fingers from each hand and you'll see exactly what proper slipping/scoring should do to your clay internally. Failing to do this will usually result in a bad joint/weak spot.

 

On the plus side, it is a good learning experience to have stuff fail/break/collapse/blow up -- you learn from it and correct how you build. When you make successful art all the time you're really at a loss because you don't learn from the failed attempts. When you open a kiln and find all your expectations thrown out the window and you dislike the work, THEN you're learning because now you have a stronger drive to do it right the next time, and hopefully learned what not to do in the process. Failed attempts seem to make your learning grow exponentially in my experience.

[Matt Oz]

One way to tell if you're successful joining parts, is when the assembled piece is almost greenware and you can still see some moisture in the clay, look were the parts are joined, if one section looks like it's drying faster than the other at the join, then the parts are not bonded. Successfully joined parts will swap each others moister and dry evenly were joined.

[Melissa M.]

Thanks so much for the helpful replies, guys!

 

Reading through your replies, I think I may not have scored deep enough, and did not apply enough pressure (for fear of squishing my work). I'm not sure if I applied enough slip either. The joining piece that I am working with is small (about 3/4" in size), so I think that is making it more difficult for me. And I can't really add coils of clay, as it needs to look like one piece is sitting on the other (as opposed to looking like one piece).

 

So, if I did not score properly, will the paper pulp paste still work to adhere the pieces now? 

 

Melissa

[Diane Puckett]

I have known potters who successfully used paper clay slip to repair broken bisque ware. Go for it. My experience with paper clay slip is to make sure you put something where you want it. After a few minutes, it can be very difficult to remove.

 

I also like to use the same clay for the slip as I am using for the pot. Otherwise, even a slightly different color can become apparent and may affect the appearance of the finished piece.

[Marcia Selsor]

Yes. Mix it up fairly thick ..maybe slightly gooier than peanut butter.. dampen the surface where you need to join.If it is dry, it will suck the moisture out of the patch before it works. You can also do this with bisque but you need to really wet it then.Put the patch on and press /squeeze together. Clean off where it has oozed out of the joint.

 

Marcia

[Melissa M.]

Okay, thanks! I will give that a try, and practice my joining as well. 

 

Melissa

[Kohaku]

Very good answers here. I'd add that this discussion from Lakeside pottery has been very useful to me....

[Melissa M.]

Thanks, Kohaku.

 

So, about how long will it take for the paper pulp paste to dry before I can bisque fire the piece? A couple of days? (Just curious, so I can have some idea of my next bisque firing.)

 

Melissa