Reli said:
M90 cones are coated with polyurethane, so I think it'd be safe to use a damp cloth. But first try brushing most of that shiat off with a painters brush.
That is correct! We have some freedom here to use harmless wet cleaners because of PU coating.
Use soft painters Nylon brush gently from center to the edge fashion. Use a damp old microfiber cloth and wipe once you removed larger particles.
Check it is wetting by looking on the other side where there is no polyurethane coating and repeat the process. If it wets the paper the PU coating is not acting as a moisture barrier and can deform if you apply pressure.
Smear pledge on a clean microfiber cloth and finish off again watching to see if that wets the paper.
On the corrugated rims of the cone paper just go in a circular fashion with the brush only. That part is very susceptible to damage.
Hope the mess didn't react on the dust caps.
I use Pledge on a Q tip to clean dust caps also. Use a little to wet the Q tip and gently work on it.
note: wet cleaning only on coated cones with no harsh cleaners that won't damage the coating