Rosetta switch to sand reduces CARBO visibility, says William Blair William Blair notes Rosetta Resources (ROSE) said yesterday on its earnings call that it would be changing its completion design for Eagle Ford wells by switching from ceramic proppant to sand. The firm says Rosetta is one of CARBO Ceramics' largest customers. It estimates Rosetta uses between 250M-400M pounds per year of ceramic proppant, and believes CARBO management was surprised by the move. William Blair believes the switch reduces CARBO's forward visibility and it lowered its estimates for the company. The firm keeps a Market Perform rating on the stock. Shares of CARBO are down 10% to $109.37 in morning trading.