Nice painting! You painted it on a cardboard, right? You mentioned above that "They are extremely difficult to draw and I can not do without a solvent"- Well, that's true. I think the difficulty was also increased because you used a cardboard, which absorbs the oil from the paint and solvent making it dry. Also, since there is no oil left on the surface, it resulted to a matte effect.. I suggest you paint it on a primed canvas for you to be able to work on it with less difficulty. :D