Wednesday, July 13, 2011

Slip to Plastic Clay - De-Watering with Vacuum Bag

The following video clips illustrate my vacuum bag process for removing excess water from my slip mixed clay body tests. This is a reasonably simple approach to achieve maximum plasticity for a clay body test, without the need for maturing the clay over a long period of time.  Using this method a small shop clay worker can easily go from wet slip to fully plastic clay in a single week. Hand mixing clay tests without the slip wetting step will not produce a body test with anywhere near its full plastic potential. If clay tests are not fully wetted the results can be so misleading as to clay working properties and be a total waste of time to prepare.

Part 1: Mixing clay slip for vacuum de-watering

The inspiration for my method came directly from The Potter's Alternative by Harry Davis who as far as I am concerned was a mechanical genius potter. The vacuum de-watering solution described in this book was limited by then available tools and materials and so perhaps anachronistic today. Nevertheless—his basic assumptions were innovative and sound and I offer my enthusiastic recommendation for his now out of print book which is occasionally available used on Amazon. I also heavily referenced Harry's book when I designed and built my double auger pug mill which I will describe in future posts.

 Part 2: Removing excess water from the slip clay.

 My vacuum water removal method does require a few exotic bits & pieces but the overall cost is not prohibitive for anyone who seriously wants to formulate & test mix their own clay body recipes. My vacuum bag was supplied by Vacuum Bagging Systems in Brunswick, ME. The owner Darryl Keil has clay working experience to support his recommendations for the required parts (including small vacuum pumps). Darryl's business supplies vacuum bagging equipment to custom wood workers as the preferred method for clamping 3 dimensionally curved veneers.
Any vacuum bag supplier servicing the wood working industry can supply the required bags and parts. The single open ended filter bag used in my system was supplied by Crosible—the same company that supplies filter cloths for my Netzsch filter press.  My system draws its vacuum from my pug mill vacuum pump eliminating the need for a separate dedicated pump.

Part 3: Vacuum bag de-watering to produce plastic clay

Turning slipped clay into plastic clay has long been preferred method. This approach removes excess mixing water quickly but does add the expense of purchasing and configuring the required parts.  I certainly believe the traditional approach is simpler and has the added benefit of exercising one's patience (well worth developing).

Mr Issac Button, the last great English country potter, used traditional methods in his pottery—including de-watering slip to make plastic clay. My post illustrating the virtue of Mr Button's time tested method, is inspirational and a must see.