This unique drawdown blade applies a series of stripes with thicknesses in equal percentage steps, to permit single-drawdown exploration of the widest practicable application range. In addition to the hiding level of the coating, it also facilitates examination of the effect of film thickness on drying speed and surface uniformity, allowing a quick characterization of the essential features of the coating. The individual stripes are identified by “INDEX” numbers (20 to 48) engraved on the instrument, and also printed on the Form 23B Logicator Chart designed for use with this applicator. The Index Numbers are in equal numerical steps corresponding to increments of approximately 20% in notch clearance, film thickness and spreading rate.
Test Procedure: After the applied coating has dried, the operator locates the critical stripe, visually or photo metrically, and encircles the parameter of interest, as illustrated. It is generally accepted that the hiding power endpoint is not total visual extinction, but a degree of contrast just short of complete hiding, corresponding to a photometric contrast ratio of 0.98.
ASTM D 5007: In this standard, the hiding power of the wet film and then of the dry film are observed visually, and the percentage increase or decrease is reported.