3D-printing artifacts on a slip cast bottle. Are these a problem?

In this case, they are not. Here is why. The dark one is M370C with 10% added raw umber. The other is M370C. Both are glazed using GA6-B Alberta Slip amber transparent - the color difference between the two bottles is entirely a product of the difference in color of the fired clay body underneath the glazes. The wood-grain texture on the right is the artifact of 3D-printing, the case mold was printed flat rather than upright (strangely, that is the bottle people want!). But the production bottle is the one on the left and the stair casing is barely visible. Additionally, these are prototypes, the production molds would likely be made by casting a plaster model of a bottle half, smoothing and soaping it, attaching it to a clamping baseplate and then setting up the 3D printed railing around it.

Related Pictures

This GA6-B glaze is better than beer bottle glass

Ceramic glazes are actually just glass. But they are not like bottle glass. The latter is formulated to work well in forming machines (harden quickly), melt and stiffen quickly, have low melt viscosity and resist milkiness and crystallization on solidification. The chemistries to accomplish this have adequate resistance to leaching and adequate durability for a single or few uses. A stoneware glaze melt needs to be much more viscous (to stay put on vertical surfaces). And, it must have a much lower thermal expansion (to match common clay bodies). And, it must resist crystallization more much (since it cools slowly). Fortunately, meeting these needs brings along big benefits: Greater durability, hardness and resistance to leaching. Common target formulas express typical oxide formulas of glazes. Stoneware glazes and bottle glass share a common trait: They have about the same amount of SiO₂. But the similarity ends there, stoneware glazes have:

-High Al₂O₃. Three to five times more! It is the key oxide to producing durable glass. And it stiffens the melt (that disqualifies high levels from bottle glass).
-The same fluxes (CaO, MgO, K₂O, Na₂O). But they distribute very differently (half the CaO, half to one third the KNaO, much more MgO). Other fluxes like SrO, Li₂O are also common.
-Low KNaO (which they call R2O). In glazes it produces crazing, 5% is a typical maximum. But bottle glass can have double or triple that (the high thermal expansion is not an issue and its cheap source materials supply lots of melting power).
-B₂O₃ melter. It is expensive but can be justified because the glaze is just a thin layer. Glazes at the low end of the stoneware range have 5% or more boron.

The ceramic bottles shown here are made from a dark burning stoneware, the glaze is GA6-B. On the left is the same glaze on a porcelain mug. For the above reasons this glaze is more durable and leach resistant that regular bottle glass.

Links

Recipes	GA6-B - Alberta Slip Cone 6 transparent honey glaze An amber-colored glaze that produces a clean, micro-bubble-free transparent glass at cone 5-6. Works well on brown and red burning stonewares.
Typecodes	3D printing problems 3D printing for mold making in ceramics requires determination and skill. And a memory for the many problematic techniques.
Glossary	Slip Casting A method of forming ceramics. A deflocculated (low water content) slurry is poured into absorbent plaster molds. As it sits in the mold, usually 10+ minutes, a layer builds against the mold walls. When thick enough the mold is drained.

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