Drawing leads from soft (6B) to hard (6H) are sharpened flat and pushed across the film at 45 degrees, as in ASTM D3363. The rating is the hardest lead that does not cut or gouge the coating. Most cured powders land around H to 2H. A softer reading than normal on a familiar product is an early sign of undercure or contamination.
Pencil hardness is only HB today, it's usually 2H, I don't trust the cure on these.
Also heard as
- pencil test
Related terms
Impact test
A test that drops a weighted punch onto a coated panel and checks whether the film cracks or lifts.
Undercure
A film that did not get enough time at temperature to crosslink fully, so it looks fine but performs poorly.
MEK rub test
A cure check that rubs the film with a cloth soaked in methyl ethyl ketone and rates how much softens or rubs off.
Fingernail test
The rough floor check of cure: dig a thumbnail into a cooled part and see if it marks.