One factor that favors a Volquez about-face is Pirates pitching coach Ray Searage, who has received a lot of credit for Liriano and Burnett's recent success. Another is the Pirates catching situation, which features Russell Martin and Chris Stewart, two of the best pitch-framers in baseball. Rookie Tony Sanchez also figures to be strong in that category if he should make the roster.
Why is this important? Well, there are four catchers that have caught at least 20 Volquez starts, and the difference in his results are drastic. Focusing only on strikeout and walk rates, this is what we see.
Using data from 2008-13, Grandal has rated as one of the best pitch-framers in baseball, and Bako was also very good. Hundley and Hernandez have consistently been well below average. These aren't huge samples, and there are plenty of factors at play to muddle the data.
Regardless, the differences are striking. Using kwERA, a incredibly simple ERA estimator developed by GuyM and Tom Tango, there's a difference of almost a full run based on his results with Grandal/Bako and Hernandez/Hundley. If the Pirates are placing a bet on Volquez based in part on this information, it's not a bad one.