Why is it not recommended to use iron wool on unfinished wood?

Using iron wool on unfinished wood is particularly problematic due to the potential for iron stains to develop over time. When iron wool comes into contact with moisture—either from the air or applied finishes—it can corrode and create rust. This rust can easily penetrate the wood fibers, leaving behind unsightly marks and discoloration that are difficult to remove. This is especially concerning for unfinished wood, which is more vulnerable to absorbing these contaminants compared to wood that has been treated or sealed.

While the other concerns regarding an uneven appearance and the pulling up of the grain are valid, they are secondary to the issue of rust staining, which is a more immediate and permanent concern for the integrity and aesthetic of the wood surface. Therefore, the most significant reason for avoiding the use of iron wool on unfinished wood revolves around the long-term consequences of rust formation and resulting stains.