An Introduction to Slip Casting Ceramics with Multi-Piece Molds

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Potter Linda Gates decorates her ceramic surfaces using commercial digital decals with imagery of everyday objects from the 1950s, including the paper dolls of that era. It was a project she started during her studies in the ceramic design program at Bath Spa University in England. Gates prefers to slip cast her forms so that the surfaces are as smooth as possible for the decal application.

Today, Gates walks us through the slip-casting process for one of her jug forms using a four-piece plaster mold for the body and a two-piece plaster mold for the handle. – Jennifer Harnetty, editor.


 Fitting the Pieces Together: An Introduction to Mold-Making and Slip Casting

by Linda Gates

Ceramic decals can be applied to any glazed object, but it makes life easier if the ceramic form has smooth surfaces to avoid the problem of trapped air creating bubbles and holes in the image. The ceramic form shown here is a slip-cast jug that I designed as part of a college tableware design project.


Mold Making and Slipcasting 101

Molds are a simple way to create simple or complex forms and make multiple copies of them with little effort. With the construction process simplified, the individual forms lose their preciousness, which allows you the freedom to creatively experiment. In Fundamentals of Mold Making and Slipcasting, Guy Michael Davis leads you step-by-step through the entire mold making and slip casting process.


1slipcast02With a little modification to the original jug design, I made new plaster molds, one for the handle (figure 1) and the other for the body of the form. The mold for the body of the jug (figure 2) is made in four parts – the two sides, the base, and the reservoir.

2slipcast03To prevent leaks when pouring the casting slip, secure the parts firmly together with strong bands cut from rubber inner tubes (figure 3). If you design your mold to include a reservoir, which makes it easier to maintain an even rim thickness, fill the mold to halfway up the reservoir wall using commercial earthenware casting slip. As the porous mold absorbs the water from the clay, the excess is drawn from the reservoir.

3slipcast04The handle mold is also filled with casting slip. Once the slip is the desired thickness (check by blowing on the edge of the mold where the slip and plaster meet), pour the extra casting slip back into the container and leave the mold inverted at an angle to drain into a bucket. Placing it at an angle avoids stalactites of clay forming on the bottom of the piece.

Tip: To achieve even thickness between multiple casts, it is a good idea to time the first casting and use this as a guideline.

4slipcast05When the mold is well drained and the sheen has gone from the wet casting slip (typically about 20 minutes), remove only the reservoir portion from the jug mold, trim the excess clay from the top and clean it up with a damp sponge. I leave the rest of the mold intact for a further hour or so for the form to firm up for easier handling.

5slipcast06Both molds are then disassembled and the jug form and handle carefully removed. Both component parts are cleaned up with a fettling knife and damp sponge. The handle is attached, and the form is covered in plastic for 24 hours to ensure a secure join.

To learn more about Linda Gates or see more images of her work, please visit www.lindagates.net/.


Comments
  • I’ve just purchased The Clay Lovers Guide to Making Molds & The Essential Guide to Mold Making and Slip Casting. I’d love to see a (2) piece mold making video!

  • Very Cool Stuff, Linda Gates. Quite different from the “Engage” bottles I have from your days at Irvine Fine Arts Center. I like the new work just as well. I found more online as well. Joe Viers

  • Very interesting process. I have often been interested in making a mold of pottery pieces that I have hand built. Can you offer some references on how to make plaster molds?

  • Hi,
    I am interested in making multiple piece molds as well. I need help understanding where the undercuts are and how to determine where to draw the lines for the multiple pieces of the mold and the best design for input &output of slip.

  • Yes, I would also like to see mold making. How do you get those registration holes and how do you know where to break up the mold? And how do you do that?

  • Thank you for this great article. You indicate using commercially prepared slip. I am wondering if it is possible to make a good casting slip from my recycled and reclaimed clay. Do you know what would be the indicators for an adequate slip if I made it myself?

  • To Dr David who asked for info on how to make molds: you just have to click on the right of this article, on the item “making ceramic molds” inside the list “Pottery making techniques”.

  • I am interested in the decal part of this post…I would like to make a small number of commemorative mugs for a local event, and thought decals of an old photo would be great. Can any one help me with this? Can I make my own on a copier? Resources? In simple words? Thanks!

  • Also, go to your local library, there are many books on pottery techniques where you’ll find details on how to make complicated molds. Plus there must be all sorts of resources online.

  • Hi,
    I am interested in making multiple piece molds as well. I need help understanding where the undercuts are and how to determine where to draw the lines for the multiple pieces of the mold.

  • I make my own decals using a laser printer and decal paper that you apply and heat set in a oven at 350% they are microwave and dishwasher safe.

  • Bel decals instructs to fire toner decals at 06 on glaze. I have not had very consistant results. Is there someone that has a full proof technique?

  • An excellent resource for anyone wanting to make simple or more complex molds is Andrew Martin’s book The Essential Guide to Moldmaking and Slipcasting. I learned just about everything I know from this book and it would answer any of the above questions from making slip to making molds.

  • Genevieve is right – for those asking about mold making (and Sultans q regarding glaze) have a look at the links to the right of the article.

    For those asking about decals, use the search function at the top right of the page – lots of info at your disposal.

    Seek and ye shall find!!

  • toner decals may be baked on to the piece at 350 degrees but are not permanently on unless you take the glaze to a melted soft so the it is melted into the glaze. Oven applied will most likely peel off eventually, I would think. Especially if you are going to sell the piece with the decals on it. Here is some info from a very accomplished potter with decals
    http://blog.mudstuffing.com/ top right hand is resources for decals lots of info.

  • I would like to add this to the mix. I work with molds that are brand new to being almost worn out. I work with at least 10 -15 different casters at any given time. Using the time method is not practical. I teach them to watch the pour and every 15 min. to add more slip, this creates rings like on a tree and you can gauge the thickness that way. We go from approx. a nickel thickness to 1.5 inch depending on the piece. This has worked very well for all of us, and I don’t have to babysit. Its pretty tried and true.

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