uriart,
I looked at material in my possession and unfortunately nothing like a Shishkina not found. Plus the fact I do not see the emphasis of his signature. "Sch ..." I saw and the signature in my opinion is not typical. My opinion - a Western painting.
And. Yuri! I never give advice and not comment on those who are "cooler" to me. I myself am learning from them. In this case you. You yourself by trial and error have a good collection of Russian and Ukrainian paintings. I have great respect for "practitioners" as opposed to "theoretical", so I ask my conclusions on your work considered "friendly correspondence"