ASTM D7899 Standard Test Method for Measuring the Merit of Dispersancy of In-Service Engine Oils with Blotter Spot Method
6. Apparatus
6.1 Positive Displacement Pipette, Class A to deliver 20 µl.

6.2 Filter Paper, having the following characteristics:
Paper density: 84
Paper thickness: 0.16 mm
Type: Qualitative
Particle retention: <2 µm
Filtration: Slow
Filtration Herzberg: 750
Material: cotton liners and cellulose

NOTE 2 - The filter paper characteristics are critical for the quality of the results.

6.3 Filter Paper Holder, made of two parts of rigid material, with 50 mm +/- 1 mm holes, the filter paper is positioned between the upper part and the lower part. The minimum distance between the holes shall be 65 mm to prevent the oil spots from overlapping. See Fig.3.

6.4 Oven, capable of maintaining a temperature of 80 °C +/- 4 °C. It shall be equipped with shelves to position the paper holders. It shall not be equipped with forced air convection.

6.5 Dispersancy Tester, (Fig.4) shall be equipped with backlight illumination, a digital camera connected to a computer to analyze and record the oil spot image, and the ability to compute the dispersancy number according to the described method.
6.5.1 Digital Camera, associated to its dedicated software, type WVGA shall have a minimum resolution of 752 x 480 pixels.

6.5.2 Illumination Source, shall provide a uniform light on the entire surface of the oil spot.

6.6 Neutral Density Filter or ND Filter, for instrument calibration, to be used to reduce the intensity of light by a definite ratio, without affecting the tonal rendition of colors.
6.6.1 Neutral density filter with 50 % light transmission.

6.6.2 Neutral density filter with 10 % light transmission.

NOTE 3 - Kodak (trademark) Wratten2 filters have been found satis-factory for this application.

6.7 Reference Spots, two reference spots printed in black on the filter paper specified in 6.2, one with a diameter of 35 mm +/- 0.2 mm, one with a diameter 20 mm +/- 0.2 mm.

NOTE 4 - A special calibration kit including the two filters and two reference spots is available from the instrument manufacturer.