Sandblasting

[Daniel Spruyt]

Sandblasting

As announced in the discussion about water etching, I will describe my -limited- experience about sandblasting.
Sandblasting can be applied on bone-dry unfired clay, bisque and, on glazed surfaces.
Depending the technique used to erode the material away, sandblasting on bone-dry clay can be quite fast and dramatic regarding the amount of clay removed. One can easily pierce the wall of a pot if one is insisting on a single spot.
On bisque fired objects, the process is less aggressive and may to some extend be compared to water etching bone-dry clay.
On glazed objects, the effect is even more attenuated and is merely matting the surface as e.g. matting glass. In fact this is what you do: etching glass by abrasion.

Regarding equipment, there are roughly 3 types of interest for ceramic work.
1) The so-called 'air-eraser'.
This is a small tool resembling much to an airbrush and allows fine, detailed work . The abrasive ('sand') is very fine Aluminum oxide.

2) The bottom feed sandblasting gun.
This tool resembles a classic bottom feed spray gun, siphoning the 'sand' out of the attached container and projecting it through a rather large orifice.
The sand can be Aluminum oxide of a coarser granulometry than for the 'air eraser'. As the 'sand' cannot be easily reclaimed, the cost of the Aluminum oxide may be a restriction. I use white, sharp quartz sand, this is cheap and can be obtained as sand for masonery.
The tool is, in my opinion, the roughest to used for ceramic work.

3) The sandblasting booth.
This is a kind of 'glove-box' containing a 'sand' reservoir and a spray gun all inclosed, and the 'sand' is reclaimed continuously. This can be considered as the most 'professional' equipment and, the most tidy and harmless to use. The action will probably be as rough as the gun described in 2).


Other - more aggressive-  equipment is out of the scope for ceramic work.
One thing has to be stressed: eyes and the whole face have to be protected during sandblasting and gloves should be used as well. The 'sand' will be sprayed almost everywhere and so it is best to use a good extracting hood or to work in the open air.

The masking materials.
This is, for the moment, a bit a bottleneck. In the discussion about water etching, I mentioned that several media were suitable for masking before sandblasting. This is not true!  Robin Hopper, one of the few that mention sandblasting in his book ‘Making Marks’, mentions rubber cement as being the prefered one. Indeed, the media I tested like, shellac, wax (emulsion), paper… are not at all suitable. They are all eaten away quite quickly by the sand. I tried a latex used for naked Raku and this seems to work. The major properties of a making medium for sandblasting are:

- good adhesion to dry clay or bisque
- resilient and elastic in such way that the sand particles bounce back from the surface (by this the energy of the blast is absorbed).

A remark about fine Aluminum oxide: This fine powder used in the ‘air eraser’ should be absolutely dry. Otherwise, it will form small lumps and partially clog the nozzle of the eraser, resulting in very irregular etching.

So far my limited experience about sandblasting in ceramics. All comments are welcome.
In a coming post, I will show some results.
I recommend to look at the web page of Amy Cooper:
Amy Cooper

This work is outstandingly fine in detail and Amy uses sandblasting to achieve this.

[Lawrence Weathers]

can you use the white, sharp quartz sand in the air eraser?

[Daniel Spruyt]

Hi Larry,

No, this sand often used for masonry is much too coarse for the air eraser, unless you find a quality that's fine enough. Unfortunately, Paasche nor Badger give the mesh size, but on sight it must be 250-300 mesh.

Lawrence Weathers said:

can you use the white, sharp quartz sand in the air eraser?

[Daniel Spruyt]

I continue the discussion with some examples of recent sandblasting results.

In the picture below you see a bisque fired pot with - in relief- a triangle. The blasting was done on bone dry clay with the bottom feed gun using quartz sand . The masking was done with wax emulsion. Clearly the blasting was aggressive: the edges are rounded and the whole masking was damaged. 

On the following picture one can see what happens if the Aluminum oxide in the air eraser is not completely dry:

Some irregular pitting occurred . I left it like that, no masking, in the idea it might become a decorative texture.

Here also the blasting was done on bone dry clay before bisque.

Drying the blasting medium at 110°C will solve the problem.

Before pursuing this technique I also will have to obtain some rubber cement.