Viewing boxes, using a small box (usually metal) with a small fluorescent
lamp
offset from a glass window on the box top, can provide an indirect light
source.
The bottom indside of the box (under the window area) should be painted a
flat black. A magnifier of 2-4x can be suspended or moved over the agar
plate
when it is placed on the box window with the light on. The light, shining
indirectly, will tend to highlight the precipitin line. The flat black
background
immediately under will give a contrast. The magnifier will help to
enhance the
show (a hand-held magnifier can work). Other techniques I've used or
heard
of: 1. allow more time for reaction (72 hours gives clearer lines than
24)
2. put reacted plates in a 6-10 degree C refrigerator overnight,
then re-read
3. Try varying well depths &/or spacing, assuming ag/ab conc is
optimal
4. some people have used weak acids or dyes - I never had to try
that
5. or you can give up and move to ELISA or maybe nephelometry
doug
