When the condenser diaphragm has been adjusted, remove the condenser and measure the diameter of the opening in the condenser diaphragm. A disc of this size may be cut out of coloured gelatine and stuck centrally onto a disc of glass or plastic cut to fit in the filter holder. Having fixed the central disc, the remainder of the outer part may be filled in with the secondary, lighter colour. This is made as follows. After this is hard or has dried then divide the outer part of the disc into four quadrants and fix two colours of gelatine to these.
Opposite segments are of the same colour and lighter colours serve best here.
Yellow or orange and green or light blue make good pairings. When completed, the disc should look like Fig 2. A fuller description of Rheinberg illumination and the effects which it can give will be found in the RMS Handbook No. BIOS Scientific Publishers. Please try it - the results are often most impressive and beautiful.