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October 14, 2009

Thin Slips: The Key to Decorating Pottery Surfaces with Slips in the Bisque State

by Terry Gess Read Comments (17)

	Slip has many uses in the pottery studio. This liquefied form of clay can be used for joining pieces, trailing a raised design or coating a different clay body to make it darker or lighter. Most often, slip is used on clay in the green state, but potter Terry Gess does things a little differently. He uses slip to decorate his pottery surfaces when they are in the bisqueware state. He likes the freedom that comes with knowing he can experiment and if he doesn’t like the results he can just wash it off and start over. But there are technical challenges to this method. Today Terry explains the challenges and the method he has developed to overcome those challenges. He also shares three of his slip recipes. - Jennifer Harnetty, editor.
The challenge and subtle beauty of slips are of great interest to me. Potters firing with salt, soda or wood kilns often employ slips on the exterior surfaces of their work to achieve thin, skin-like surfaces. Slips are related to glazes, but they are comprised primarily of kaolin and will record the nuances of the kiln’s flame, combustion and atmosphere. The result can be similar to the blush on a peach or the subtle patina of a weathered wall. It is, however, a most fickle process, and results can be difficult to reproduce. On any given piece, I use up to four different kaolin clays in individual slip recipes in order to achieve subtle variations in the surface treatment. There are a number of different kaolin clays available from around the world, and they all have different qualities and benefits. I apply the slips by overlapping, dipping, layering, pouring, using wax resist, and other basic glaze application methods. I apply my slips onto bisqueware. Bisque gives me the opportunity to experiment, make mistakes, and to change my mind and wash everything off without destroying the pot. The greatest technical challenge to this approach is shrinkage. The slips need to be watery-thin. (If the slip looks wonderfully thick and creamy in the bucket, then it’s much too thick for bisque.) I standardize the process by using a gram scale and graduated cylinder in order to carefully measure and record the specific gravity, or weight-to-volume (density) comparison of each of my slips. To measure the specific gravity, divide the weight of a given volume of your slip by the weight of the same volume of water. Most of my slips are 1.2 specific gravity (meaning they are 1.2 times as dense as water), while most glazes are in the 1.6 - 1.7 range. Adding approximately 2% Veegum Cer (which is a mixture of synthetic and natural gums) and 1% bentonite to the slip helps with glaze suspension and also binds each layer of slip to preceding layers on the surface of the pot.
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Helmar Slip Nepheline Syenite . . . . . . . . .  15 Grolleg Kaolin . . . . . . . . . . . .  20 Helmar Kaolin . . . . . . . . . . . .  65 Add:    Veegum Cer 2            Bentonite 1   Tile 6 Slip Nepheline Syenite . . . . . . . . . . . . . .  20 Calcined EPK Kaolin . . . . . . . . . . . .  20 Tile 6 Kaolin . . . . . . . . . . . . . . . . . . . 50 325-mesh Silica 10 Add:    Veegum Cer 1            Bentonite 2   70/30 T6 Slip Nepheline Syenite . . . . . . . . . . . . . .  30 Tile 6 Kaolin . . . . . . . . . . . . . . . . . . . 70 Add:    Veegum Cer 2 To see more images of Terry Gess’s work, visit www.terrygesspottery.com.
This post is an excerpt from a full article on Terry Gess and his work in the November 2009 issue of Ceramics Monthly. Get great articles like this in glossy full color delivered right to your door! Subscribe today!

 

Tags: Ceramic Decorating Techniques, Salt Firing, Terry Gess

17 Comments

1. ayala | October 14th, 2009 at 10:35 am

   can u use slips in gas kilns or electric?

2. Zygote | October 14th, 2009 at 10:56 am

   Your surfaces are lusciously warm… beautiful work Terry.

3. garth | October 14th, 2009 at 11:25 am

   What temperature are these fired to, and in oxidation or reduction?

4. Eudora | October 14th, 2009 at 12:06 pm

   Very nice results.

   Two questions: Is the work shown fired in reduction, oxidation, soda, etc? What cone? And, regardless of how the pieces shown were fired, does this technique work in oxidation at cone 6?

   Eudora

5. ayala | October 14th, 2009 at 12:19 pm

   I’d also like to knowwhat is or is not applicable to electric firing/with what adaptations/and at which cone.

   nice to look at-wish there was a way to recreate the visual softness with electric…..

6. dawn | October 14th, 2009 at 12:37 pm

   Ditto the comments above: electric?, gas?, cone?, etc. Your work is so much in line with my sensibilities. Truly lovely.

7. Lynne | October 14th, 2009 at 1:54 pm

   I also would like to know what type of firing is used, and if you have ever raku or pit-fired with this slip-on-bisque. Also cone? I love this work of yours - the surface technique and the pots, too!

8. Elaine | October 14th, 2009 at 3:01 pm

   For bisqued work, I have always just made slips from the same clay as the body, diluted with water, sieved and coloured with stains- no sweat and no problems- then glaze normally.( I work in earthenware).

9. Elaine | October 14th, 2009 at 3:03 pm

   PS- forgot to say, electric kiln, from 1060- 1120.

10. Genevieve | October 14th, 2009 at 7:50 pm

    Good article and thanks for sharing your recipes.
    For all the people with questions : experiment! experiment! experiment! experiment yourself, and you’ll discover wonderful results that are your own and only yours.
    There is no reason why these slips can’t be used in an electric kiln or a gas kiln or an oil kiln, or a wood kiln of course. The difference in results will be obviously linked to the type of kiln and firing (reduction or oxidation) just as they are for the clay body and the glaze. There is no magic bullet.

11. judy | October 14th, 2009 at 11:48 pm

    I love this. It gives me so many ideas. may we never stop trying different things.

12. Carole | October 15th, 2009 at 9:24 am

    I echo Genevieve’s comment. TEST! TEST! TEST! With this basic idea, I will try it out by adding a “test” piece to a regular kiln load. Eventually I will come up with the right solution for my work. Thanks for sharing, Terry. Your brush work is wonderful!

13. Ben | October 16th, 2009 at 2:20 am

    Thanks to Terry for the great article. The work you’ve put into your slip shows. Quite impressive!

14. Sulayman | October 16th, 2009 at 2:54 am

    Genevieve has spoken mind. All you need do is experiment yourself and you’ll discover many other outstanding results that could even surpass the current one.
    I however salute Mr. Terry for the G_R_E_A_T work. We’ll all try to emulate you by trying out the methods and the recipes you were so magnanimous to dish out. thanks and more grease to you noble elbows!

15. Sulayman | October 16th, 2009 at 3:01 pm

    Genevieve has spoken my mind. All you need do is experiment yourself and you’ll discover many other outstanding results that could even surpass the current one.
    I however salute Mr. Terry for the G_R_E_A_T work. We’ll all try to emulate you by trying out the methods and the recipes you were so magnanimous to dish out. Thanks and more grease to your noble elbows!

16. janice | October 17th, 2009 at 6:14 am

    beautiful effect Terry…are you trying out various Mason stains for your colorants?

17. Terry | October 18th, 2009 at 9:05 am

    Thanks to everyone for the kind comments regarding my work — we have great camaraderie in the clay community!

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