A closer look.
The 3x1 inch slide cover has been removed and the forams photographed in peripheral reflected tungsten light from an arrray of four 2.2 volt torch bulbs.These were connected in series and controlled by a 9 volt Russian microscope light power source.
The prefocus bulbs have been mounted on a board in standard holders on short stiff wires so that they can be individually directed at a central target.
The tungsten light has been chosen because it can be compensated in the Canon Powersot A20 camera.
A database has been created with references to plates in Murray's 'Atlas of Foraminifera of the British Isles'.
Under higher power it can be seen that perimeters of the little black circles were drawn with a fine compass. Some of the central pin marks can be seen and the centre is filled in with black of a slightly different shade. There are also occasional places where the black is missed, revealing a sight of the white base.