Iron and slag glass lamp

Inherited this art nouveau lamp from my grandmother. It’s been in the family almost a hundred years when my great grandmother came to America from Italy. It’s a 6 panel slag glass and iron electric lamp. There is a foundry mark that appears to be initials RY. Can you tell me who made it and how much it’s possibly worth. All the glass is intact with no cracks in the glass or lamp. It has and electric cord and the light socket has pull chain.