| a) | The material must be absorptive, to perform blotting action |
| b) | It must have a fine texture but not be too fine, as this may block imperfections |
| c) | For colour contrast penetrants it must mask out background contours and colours |
| d) | It must be easily and evenly applicable |
| e) | It must form a light and even coat |
| f) | There must be no fluorescing of the developer when used with fluorescent penetrant |
| g) | The penetrant bleeding from a discontinuity must easily wet the material |
| h) | When used with a colour contrast penetrant it must be of a highly contrasting colour. It seems agreed that the best colour is white |
| i) | It must be readily removable after the test is completed |
| j) | It must be non-toxic and non-irritant |
