While overseer of Egypt, Thistlewood began to acquire slaves, whom he then rented out to earn an additional income. All his slaves were branded with "TT" on their right shoulders. When Bess's son Bristol was seven, Thistlewood had him branded. When Mary was recaptured after running away, Thistlewood had her flogged, branded on her left cheek, and "put her on a steel collar with a few links of chain to it". By 1762, he owned 12 slaves. By 1767 he owned 28.