Hi my name is ***** ***** you for your question. In today's art market value is driven by the artist. If he or she is listed, collected etc. With an unsigned work the challenge is to identify the artist, which takes many hours of research. You can go to the art history department at the local University for help. The other work by Frans Vos. I made a quick search through my art data base and found names that are close. Usually Vos is spelled with two s's or preceded by a de as in de Vos. Do you have an image of the painting and the signature you can send? You can attach them using the paperclip icon found on the tool bar. I will be on Holiday Mon. & Tues. so there is no rush getting them to me.