Classic Medalta Potteries Beer Bottle Mold

Making a new mold using 3D printing

The original bottles were hand thrown and very heavy. This one, for example, weighs 525g. Our bigger slip cast equivalent with a modern shape, 3mm thick walls and much higher capacity weighs only 400g.

The color, enduring glaze fit and the type of clay used by Medalta indicates these were likely fired at least to cone 10. Energy was cheap at the time and the Saskatchewan clays they used require high firing.

This is a test mold to determine if the swing top stopper will work on a neck of this shape. This mold only weighs 87g and the walls are printed to only 0.8mm thickness. Two natches are sufficient to keep the halves aligned perfectly. Pieces will shrink about 12%, thus the larger size. We will use tissue transfers for the decorations, the GA6-B glaze for the inside and shoulder and G2926B transparent for the body.

Related Pictures

Finished cast v1 stoneware beer bottles

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The center bottle is a standard glass one, the other two are ceramic, cast out of my version 1 plaster mold. The stopper fits perfectly. The clay is Plainsman M370 + 10% raw umber, it fires black. The glaze is GA6-B, an amber transparent that produces a deep glass-like effect over the dark burning body. They were fired using the C6DHSC firing schedule. These bottles are a testament to how 3D printing and 3D design now make it possible for even casual potters to make pieces never before practical or even possible.

An 85-year-old Medalta Thrown Beer Bottle:

How can it be so white, speck-free and uncrazed?

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These (right) were made individually in the factory during the 1930s and 1940s (the insides have pronounced throwing rings and slip drips). The potters were able to make up to 500 per day, even though they took the time to smooth the outside using a rib! The inside base of this one is bowl-shaped (the walls near the base are very thick), this helps explain how they were able to throw them so quickly.

Perhaps most surprising is how much whiter and speck-free the bottle is even though it is fired four cones higher than the crock (Plainsman M340 at cone 6). Both pieces have porosities above 2%. Why? First, they got their clay from further east in Saskatchewan (near Willows), where the cleanest clays are much lower in iron contamination (likely the H0009 body). The whiteness is better even though they would have had to add some ball clay to make the clays more wheel-throwable. Second, they employed a wet process to refine the clay (slaking, blunging, sieving and filter pressing), this enabled them to sieve out the iron pyrite particles. Fortunately, modern dry grinding and air separation equipment is greener and able to accomplish without water.

Notice also the transparent G1129 glaze on the beer bottle (the upper section is likely the same glaze stained using iron oxide): After almost 100 years it has not crazed. This is both a testament to the ease of glaze fit these natural materials offer (because of the high quartz content) and the skill of the engineers of the time at matching the thermal expansion of glaze and body.

OnShape CAD is Free for Hobby Makers:

Is it as good as Fusion 360?

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It is very hard to let Fusion 360 CAD go. But the approaching $750 renewal is powerful motivation! OnShape is amazing. There is nothing to install, it runs in a browser tab like Google docs (see picture below). Sure, it won’t run offline, but I am almost never offline. It functions very similar to Fusion 360 for my basic requirements of making molds for slip casting. Recent experience with the complexity and slowness of Solidworks for Makers, which is total overkill for what I need, really makes OnShape look good.

My OnShape drawings are stored in my cloud account and are public. That sounded bad at first, but it also means that they are shareable with others (another person, whom I choose, can actually work on a drawing at the same time as me). The full OnShape is working in Firefox on my 2014 Mac Mini Ubuntu Linux machine. This is beyond exciting to me, traditional CAD has always required expensive hardware that is far beyond a hobbyist (of course, OnShape will also work in Safari on Mac and Chrome on Windows). A real bonus: I can edit drawings on iPad in what appears to be full power mode (although a mouse and keyboard are needed for serious work).

Besides the above, here are some of the features and advantages I am seeing:
-It opens and saves many professional CAD file types (a major drawback in SolidWorks for Makers).
-It is really fast, login is quick and a drawing can be open in seconds, this is way better than xDesign for Makers (from Solidworks).
-Documents are always saved, close one by simply clicking the home icon on the upper left.
-The timeline (called the "Feature Tree") can be reordered, turned back and has folders like Fusion 360.
-To 3D print just select part of your drawing, right-click and choose to export it in 3MF or STL format (it goes into the downloads folder).
-All tools are in one long, monochrome ribbon of tiny icons at the top but there is a tool searcher.
-Like Fusion 360, sketching constraints are inferred as sketches are created and applying them works in a similar fashion. Their tiny symbols display in groups and associate to the point or line by a light grey line. Automatically applied constraints can make sketches behave in strange ways until you learn to find and remove the offending ones.
-Constraints and dimensions are movable so drawings can be uncluttered for printing.
-Section analysis is in the "Camera and Render Options" pop-up under the view cube.
-The spline and bezier sketching tools are not as interactive (a downside of running in a browser).
-Parameters, called variables, are more in your face; they are even shown in the timeline.
-Panning, rotating and the viewcube work a little differently. The iPad version of OnShape beats Fusion easily in this respect.
-OnShape does appear to support text along a path like Fusion.

The secret weapon of learning OnShape: An AI chatbot. Just ask any question about how to do something. One helpful migration from Fusion 360 is to print the sketch(es) (with constraints and dimensions) and work from that to create the equivalent in OnShape. An advantage of OnShape is that if you get stuck (e.g. drawing goes red), you can share a link with a more knowledgeable friend to tell you what is wrong. Most often the issue is conflicting constrains.

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