This story was excerpted from Justice delos Santos’ Pirates Beat newsletter. To read the full newsletter, click here. And subscribe to get it regularly in your inbox.

Mike Burrows already possesses one of the most aesthetically pleasing breaking pitches among the Pirates’ pitching prospects, a biting curveball that completely falls off the table when working right. For his entire professional career, the curveball has been the only breaking pitch in his bag, but this season, he’s adding another one into the mix.

Burrows, the Pirates’ No. 9 prospect per MLB Pipeline, is incorporating a slider into his repertoire. The slider remains in the research and development stage, but Burrows hasn’t been shy about using it this spring. Through two appearances, Burrows has thrown eight sliders, eight changeups and six curveballs.

“I wouldn’t say it’s anything yet,” Burrows said. “I don’t know how it’s going to fit. I don’t know if it’s going to be more of a predominant pitch or if it’s going to be something that’s more of a set-up pitch. I haven’t really figured all that stuff out yet, and I really just need more reps in-game against live batters and see what the hitters tell me, see what the catchers have for me."

The sample size is far too small to make any determinations, but the results have been mixed thus far. In his first outing of Spring Training, Burrows threw four sliders -- all balls. In his second outing, Burrows generated two swing-and-misses and a groundout but allowed a single as well.

Burrows initially planned to add a slider to his arsenal last season, but he opted to master the three pitches he already had in his bag -- fastball, curveball and changeup. Prior to this spring, he decided to start throwing the pitch, a decision that the Pirates supported.

“It hasn’t been hard yet," Burrows said. “That’s been something I was hoping for. After putting so much work into a pitch throughout the offseason, it was nice to see that I was getting some bad swings.”

The Pirates added Burrows to their 40-man roster this offseason, bringing the 23-year-old one step closer to making the Major League team. If all goes well to begin the season, Burrows could be showing off his new slider in Pittsburgh by the summer.