How to Construct Cottle Boards for Plaster Mold Making and Slip Casting

This video was excerpted from Fundamentals of Mold Making and Slip Casting, with Guy Michael Davis, which is available in the Ceramic Arts Daily Shop.

My new year’s resolution is to make more molds. Molds are a simple way to create simple or complex forms and then reproduce them with little effort. When you do this, the individual forms lose their preciousness, which allows you the freedom to creatively experiment.

With the little studio time that I get, I definitely fall into the habit of letting pots become too precious and sticking to what’s “safe.” If you do too, today’s video may be just what you need. In this excerpt from Guy Michael Davis’s Fundamentals of Mold Making and Slip Casting, Mike demonstrates his simple and easy method for making cottle boards.   – Jennifer Harnetty, editor

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To learn more about Guy Michael Davis, and see what he’s up to in the studio, please visit his blog: http://guymichaeldavis.blogspot.com/.


**First published in April 2011
Comments
  • Good video clip. I cut cottles from laminated countertop sink cutouts (most cabinet shops will give them to you) and they work great also. The laminate facing inside of course…the plaster does not stick to it. Thank you CAD.

  • Thank you. This gives my DH a better idea of what I have been telling him to make for me to be able to make molds.

  • This is a great little demo. I have been using these for many years, since my patternmaking days. We called them “dike boards”, and kept ours covered with “goose grease”. Mine are 1/2″ birch plywood, with pine or fir 2X2’s at one end of each board.

    “Goose grease” is made by warming up a pan of kerosene, and adding stearic acid until it no longer dissolves into the kerosene. This is the traditional plasterer’s parting agent, but it must be warmed up before each use. Tincture of greensoap 50/50 with water works almost as well, but goose grease sets upon contact, and has more “body” than soap solutions.

    I sincerely hope your upcoming plaster demo includes the correct method for mixing plaster. There are many WRONG ways and one “best” way.

  • if you gonna tease us w/ an excerpt , at least give us something! like Pete suggested –plaster mixing! etc.
    if cottle board fabrication needs explaining , maybe moldmaking might not be yo cup-o-tea!

  • If you are going to make small molds…like for appique items or jewelry pendants, you can use plastic containers like Glad food savers. Bigger plastic containers can be used to make molds also. I have done this. It is simple and quick. I like many things that I see on the videos on this site but there are times, the people making the videos take a long and overly involved method to get results that others get using other types of equipment…but to each his own.:)

  • My experience with glued joints in furniture is that using either dowels, or biscuits, with the glue, will provide a stronger joint against shearing forces than just glue alone. Also, a water resistant glue – like Gorilla Glue – might be a good idea.

  • To those who think a video about cottle making is unnecessary: how did you learn to make them? You saw someone do it, of course! For people who are interested in making molds but do not have a course offering or artist in their immediate area, this is a great way to learn how to begin. And every one begins the same way. At the beginning.

  • Some of the comments are a little, done this before. I think it helps to see these videos as they will help people who have never done it before. I learnt to do this at college and have used plastic boxes and plastic tubes such as washing up liquid bottles, cut up the site and closed with a band. Or larger pieces of plastic sheet and rolled to make a larger tube. Anything to contain the plaster. Still good to see it demonstrated.

  • Poor timing on the video, since the night before I had poured plaster for mold into quickie cottles made of linoleum. One clay dam I made burst and made a mess, of course, when I jiggled the cottle to get rid of bubbles. Maybe now I will take the time to make some decent wood cottles, even though mold making is not a primary occupation for me. It would save time in the long run. Thanks again for another interesting video and for CAD in general. Stuff to learn (or absorb or take to heart) even after 40 years of potting.

  • I have never had the benefit of seeing a mold-maker at work and have used all sorts of weird things as cottles. Some successfully but others rather untidy. So for me and I am sure many others it was good to see and I aim to get organised with cottles. I ofen need to make a mold and dread it as it is not my cup-of-tea but sometimes yo got to do what yo got to do, so thanks Mike and CAD. For those who know it all, you don’t HAVE to watch these generous free excerpts!

  • I thought this was very good. I liked the specific measurements given and liked that he showed every step for making successful cottle boards. I used a different type when I first learned to make plaster molds. I think I will try to make some like his now that I have Mike’s clear instructions. Thanks for this and all the free videos. They really help those of us who like to learn!

  • I’ve made cottle boards in the past and am making one today. Two points: 1)I find that just using wood glue is not enough. I have to use screws to make sure that they don’t come apart. 2) I use the frame on a mirror in order to get a smooth surface, however I get leaks and have to seal the edges with clay. Does anyone have a good way to prevent leaks or to seal them.

  • Could someone please tell me what this “soap” is made of ? I’ve seen it in books etc, but living and working in Japan I’ve never seen it in reality and they certainly don’t have it for sale in the pottery supply shops here. If only I knew what it is actually or with what it could be replaced, that would help greatly. I have tried years ago with washing up liquid soap, but to no avail. Thanks for your help, anyone ?

  • To Genevieve Halse I find that the best mold release is from Smooth-On Inc. called Super Seal. I also like to use Vaseline and to thin it use Baby Oil. Both work great I have been making molds for over 40 years and have seen all kinds of mold releases and techniques. Anyone interested in making these boards, when I was first taught we made them however we used small 6 inch angles that have screw holes already in them. Screw them to the ends of the boards using a 90 degree angle.

  • In college we used melamine laminated pressboard for our cottle boards. Easy to set up with clamps, seal up with clay, and clean up afterwards with a scraper, and a sponge if necessary. For soap, we used some kind of mixture with Murphy’s oil soap. Has anybody else used that?

    By the way, I was able to learn mold making and slip casting in college, without ever haven taken the basics of pottery making. It’s not that hard, if you don’t get too complicated and you have someone show you how to do it. Undercuts are what cause the problems.

  • Thanks for this. I’m just starting to get into mold-making for the dolls I’m sculpting, and I find it absolutely daunting. This helps a lot. Will be buying the video when I start in earnest.

  • Great simple video. I’m going to make some very soon. Can someone please tell me more specifically what ‘oil soap’ is. I am in Australia, so please don’t talk in American-only product names. Ingredients please. Is it what we would call ‘soft soap’ which we use as a mould release when dealing with plaster against plaster?

  • Love the design and the versatility of these boards.

    Murphy’s Oil Soap: http://en.wikipedia.org/wiki/Murphy_Oil_Soap “Despite the name, oil soap does not contain oil; it contains potassium soap manufactured from vegetable oil. The other constituents of Murphy Oil Soap are sodium EDTA, propylene glycol, fragrance, surfactants, and water.”

    A previous post suggested screwing the blocks on to the board. A couple of tips – 1. pre-drill the holes to prevent splitting of the blocks. 2. countersink the screws and fill the holes, and sand flush. 3. use waterproof glue and you may get away without screwing the blocks on although they will be much more durable screwed together.

    To prevent leaks – putting clay coils on all the seams definitely works but of course you have to do it every time. You could get some rubber gasket material and sandwich it between the block and the adjacent cottle board – could even glue it to the block so it is always there. Would also have to make sure the blocks are sealed to the board – perhaps “liquid nails would work for this purpose if you put a continuous bead right at the edge of the block that will be exposed to the plaster. Liquid nails is waterproof so could eliminated the need for screws as mentioned above.

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