Complex sentence: When Newark's Rabin & Krueger Gallery gave Dee his first solo exhibition in 1957, he showed abstract paintings, but, impressed by Joseph Stella's silverpoint drawings, which were on display at the gallery, he subsequently transitioned to an austere style in that medium.
Split into simpler sentences: When Newark's Rabin & Krueger Gallery gave Dee his first solo exhibition in 1957, he was making paintings in an abstract style. However, impressed by the gallery's display of silverpoint drawings by Joseph Stella, he subsequently made a transition to an austere style in that medium.