Dusty oil painting

Please do not use a tack cloth. These could easily leave a residue (as they do on your hands) when in contact with the painting, which could easily discolor or even attract and hold grime to the area. Also, please do not pour water on the surface. This could do many disastrous things. It could swell a glue size layer causing the paint to flake and delaminate, or cause the fabric support to sell or even shrink causing not only planar distortion but possibly the loss of ground and paint. It is generally best to gently dust a painting using a very very soft wide brush. A large badger blender is often used in the museum world but an affordable hake brush 2-4 inches wide would certainly suit the purpose.