Following are step-by-step instructions for field testing blotter for LSD

1. Extract a section of the blotter with a minimal amount of ethanol. (enough to leave you with a few drops of liquid)
2. Put a drop of the extraction on a 4-(dimethylamino)-benzaldehyde impregnated piece of filter (or chromatographical) paper.
3. Allow to dry.
4. Put one drop of concentrated hydrochloric acid (muriatic acid will work) on one side of the paper. A colored front should migrate over the paper (concentrating the color).
5. A purple colored ring will appear (changing to blue 30-60 minutes later) if alfa or beta unsubstituted indoles are present (the whole paper will color if large amounts are present). This purple / blue coloring signifies the presence of LSD.

According to the source, this simple field test is able to detect 7.5 micrograms (ug) of lsd without a problem (typical doses were listed as 75-250 micrograms; you should get that lucky or unlucky for that matter)