Most of the time, work on paper looks very grimy because of the accumulation of dirt on the glass itself, which could easily be cleaned. You might decide to further protect the piece by changing the mat to an acid-free mat. Be sure to know what kind of glass you have on your piece as higher quality glass uses different cleaning solutions. If your frame needs dusting, a dry feather duster is preferred. Depending on the type of frame

A slightly damp cloth will work to take away the dirt – we can not stress “slightly damp”. Not all frames are made from the same material. You can test the top outer side of the frame, which is not seen as often to be sure you are not going to damage the frame.

If a poly/plastic or glossy / lacquer finish on your frame you can use ammonia-free Windex. Spray onto cloth – NEVER directly onto the frame – and wipe clean.

Regular glass – use Windex and you can spray directly onto glass, but not suggested.
UV glass – Windex, spray onto a rag, wipe glass clean.
Non-glare – Windex, spray onto a rag, wipe glass clean.
Museum Glass – microfiber cloth with no solution. If it is absolutely needed, spray either ammonia-free glass cleaner or a mixture of 50% water and 50% alcohol or distilled water onto a lint-free cloth and wipe clean.