Slip Casting, Slip Trailing and the Altered Form: O'keeffe Inspired

 I've always dug Georgia O'keeffe's watercolors. Especially Cow Skull with Calico Roses......

This time I took my inspiration to ceramic design. 

A Word on Molds

Just and example of a mold and the clay skin

     I work with plaster molds for slip casting. I have made my own...as you will see with the cow scull mold or you can buy commercial molds sold at local ceramic pottery stores or online. I will be using a mix of both my own and commercially bought molds. I will not go into mold making here, although I fully believe that making your own mold of a piece you have made yourself is far more artistic that using someone else's mold. I plan to do lots of this! Its more technical, challenging and fun.

A Word on Slip Casting

Commercial Vase Mold and My Vase Cast (the skin)

Self Made Plaster Mold of Cow Skull and the Casted Cow Skull

I began working with slip casting a while back. Slip casting is using liquid clay (specially formulated to stay liquid or deflocculated-

occurs when the alkalinity of a clay or slip is such that the clay particles become ionized. Due to the electrical charge produced, clay particles will then repel each other. Deflocculation is especially useful in slip casting.)

 Slip is then poured into a premade mold (vase, soap dish, coffee cup), sits for anywhere between 15 and 30 mins depending on the size of the piece you are working with. The slip creates a skin on the surface of the plaster mold. Molds are usually made out of plaster and plaster is very absorbent. The plaster pulls moisture from the slip you have just poured and creates the skin on the plaster in the shape of the vase, bowl, or coffee cup. You will notice when you pour in slip cast clay that it is very shiny and wet looking, once it has begun to form the skin on the plaster surface it loses its sheen and thickens. So guesstimate the thickness of the skin by looking for the dull skin that has built up. A quarter inch is a nice thickness. The rest of the slip is poured out and can be reused in another mold. Give the mold a good shake upside down to make sure all of the extra slip is out and then place the mold upside down on a gridded surface (like a gridded table) so that any extra slip can drip out...leave for about 5 mins and then turn the mold over and let it sit for at least 3 hrs for most small molds and 5-6 for bigger molds. Waiting for the piece to set and deciding how long it needs to set depends on how you plan to work with the piece after you take it out of the mold. To do slip trailing you need to wait until the piece is leather hard- the surface of the clay will be very firm but not bone dry. 

The Cleaned up Vase

Once you remove the form from the mold take a feddling knife or scraper to rough and uneven edges. Run your sponge over jagged edges to refine the form and soften edges and remove seam lines from the mold itself, so that the end result is a nice clean form.

A Word on Altering the Form

     I've taken the vase, the cow skull and a bit of artistic intuition and combined them all into one form. Its about thinking outside of the traditional form. Since I used a commercial mold for the vase I was set on changing the form to make it mine. So I went immediately to the lip of the vase and took out triangles to create the zig zag lip. I then took to the cow skull. I cut down its back until I felt the angle was just right to sit on the body of the vase. Scratching and slipping is very important in connecting these pieces that weren't originally one piece. The goal is to create a bond that is just as strong as if the pieces were one. Because clay particles are plates that sit one on top of the other and slip past one another...you need to scratch up those plates. I like to equate this to your two hands, fingers spread wide. Your fingers are the plates...the action of them spread open wide is you having scratched the clay...now clasp your hands together finger between finger and feel the bond. Have someone try to pull your hands apart...its hard. If you just put your hands palm to palm it would be easier to pull them apart. I think you get my drift. So scratch, slip -add that liquid clay! and then jiggle and add pressure to the two pieces you are attaching together. Take a paint brush with a little water...and I mean a little and go around the edge of the two connected pieces so that you are sealing the bond!

Last bit I added before the slip trailing was pushing in the ridges of the vase. I did this so that the focal point of the piece, the cow skull, didn't steal the whole show. In any sculptural piece you want to see the sculpture in the round...that means if you walked around it all sides of it would be dynamic. You don't want your backsides to like like after thoughts. So add something that will catch your eye all the way around your piece!

A Word on Slip Trailing

It is important that you use the same clay body as the clay you used to create the form that you are slip trailing on. In my case I used Mackie's Lowfire Casting Slip for the from so this is what I will use to slip trail. Waiting for the piece to firm up, but not letting it dry out is important. If you wait too long and the piece dries too much and you try and slip trail, you will find that your trailing begins to crack after the piece begins to dry. This is because the slip and your form are drying at different rates. Your form is drying faster and shrinking and your slip is pulling away. If you slip trail too early on a really wet piece you will find that your slip drips more easily. So practice with a drip or trail to see how absorbent your piece is at the time. Work fast and remember that you can use paint brushes to wipe off mistakes.

The Final Piece

Feel free to leave comments, suggestions and ideas. The next Blog will be on Glazing Sculptures with Lots of Detail.