Black goes matte

I am fairly new to oil painting and have been putting together some still lifes. I am using a little linseed oil as a medium and am not sure why some areas of the painting dry glossy and others matte (particularly in the black areas). It is all rather distracting. I would be most grateful if anyone could tell me how to remedy this and advise me how to make the black shadow deeper and a little glossier and not so grey and matte.

Thank you for your help in advance.

Yours ever,
Arthur