Block and Case

Block and Case- confusing nomenclature


The manufacture of slipcast ceramics requires multiple, reproduceable plaster molds. You need an easy way to make copies of a mold,  for two reasons:

 - A mold can only be cast a couple of times a day (due to drying cycles), so it takes many molds to make many pieces in a day.

- Molds get damaged and wear out, and must be replaced regularly.


  To reproduce molds in quantity, you need set of "molds-to-make-the-molds". In other words, you need positive molds that can be filled with plaster, to produce duplicate mold sections. In ceramics, this is called a "Block and Case."

  There seems to be some ambiguity about the use of this term. I will try to clarify "Block and Case" here, as I understand and employ the words.

  The niche world of moldmaking for ceramics is small and diffuse. It's a craft practiced around the world by few people, with little in common, so terminology is by no means standardized.

  This sketch below describes the process, from design to production. It will help to think of each step as either a positive or negative representation of the piece.


A- Model (positive): This is original master shape, scaled up to compensate for ceramic shrinkage. It is typically a plaster model, based on a drawing, made by various sculpting and machining processes.

B-. Block mold (negative): The first mold, made from the Model. The purpose of this mold is to generate the Case, but it can also be used to make a few test samples. 

C- Case (positive)- The Case is the mold that is used to make production molds. The Case is made by casting gypsum cement on the Block. There is one Case for each section of Block mold.  Traditionally,  the Case consist of two elements- the Face, which includes the positive impression of the inside of the mold, and the Rails, which create a vessel for the plaster pour,  and which form the outside surface of the Working molds. ( Cases can also be made in the form of one-piece rubber molds.) 

D- Production (or Working) mold (negative)- Molds that are used to cast the ceramic pieces. The consumable tooling used in production. 

E- Ceramic final product (positive)


  Unfortunately, these are not completely universal terms. Consulting my preferred books on the subject (see below), I find variations in the use of these words. Perhaps these represent regional, or just idiosyncratic usage. Frith (a Midwesterner with an Alfred background) and Colclough (from the UK) use "Block and Case" as I have described. Chaney and Skee, (from California) use these terms very differently. What I'd call the "Block" they call the "Model mold". They use the term  "Block mold" to mean the  Face section of (what I'd call) the Case. They use "Case" to refer to just the "Rail" component of the Case. 

  Other terms further muddy the issue. "Master mold", "Mother mold", "Master Pattern" are relevant, but not useful, as I have heard these used to refer to either the Model or the Block or the Case. 

    Making a complete Case is a major project. For smaller runs, it is often sufficient to just make a simple positive casting of each Block mold section, and forgo the Rail system (using stock mold boards or cottles instead.) The mold maker I learned from, the late W. Geoffrey Meek, referred to this as an "Impression", which I find a useful term to distinguish from a full Case..


    Head spinning yet?

   

  In a factory, there is, typically, a hierarchy of moldmaking jobs. The entry-level job is casting Working molds from the Cases- fairly straightforward production work. The best of these moldmakers may eventually move up to making the Block and Case. At the top of the heap, the most skilled and artistic job is  the modelmaker, working with the designer to create the original shapes.

      When a product is discontinued, the factory will want to archive the tooling. Properly, it is the Block mold that should get archived. It is not the Model, since this doesn't include the mold configuration. And it is not the Case, since that is a working tool in the mold shop, and therefore subject to damage. It is the Block which, if intact, has the most information in a preserved form, and would probably be the best starting point for re-introduction of the piece in the future.

Recommended moldmaking books:

Mold Making for Ceramics, John Frith, Chilton 1985

Plaster Mold and Model Making, Chaney and Skee, Van Nostrand Reinhold 1973

Mould Making, John Colclough, Gentle Breeze, 1999



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