Section: Seed abrasion
Figure 8.  Hollowed concrete trough for abrading seeds
Figure 8.  Hollowed concrete trough for abrading seeds

A helpful rubbing trough for all this is easily made with stone reinforced concrete. A long 90-degree elbow bend (short bends are not suitable) of 100 mm irrigation pipe is needed to create the hollow. This is painted with 3 coats of cement retarder which will prevent the setting of cement in contact with the pipe. An open top wooden box (oiled inside for release) is made and the pipe is suspended firmly, elbow down, in a way that it can be removed after the concrete has set. After setting, the box is disassembled and the contact zone between the cement and the pipe is soft and can be flushed with water to expose the stone reinforcing. A wire brush works even better.

I have three such moulds, a small stone (most aggressive), a medium stone less so, and a smooth cement (no retarder applied to the pipe, instead oiled for release, and no stones). When fine (dry) rubbing is needed I add sandblasting sand (it is sharp) or the grit that is used in making sandpaper (sharper still – it can puncture the skin slightly and is available in different grades) – they both still get blunt. I find the sandpaper grit the best. A wadded piece of cotton cloth is used in the rubbing and the width of the hollow should be 100 mm to allow a fist gripping the cloth to move freely back and forth. The less aggressive abrading rubbing trough is used for removing the elaiosome and the non-aggressive plus grit is for the removal of the fine inner coat. The most aggressive is useful for separating other seeds, for example Erica and grasses, when there is a lot of dried matter. Sieves and a brush are essential helpers.