I don't see where there is any toxic chemicals used for rust bluing. With certain rusting agents you have to wear gloves, but that is for fingerprints, only. It does take longer in the winter months because of the humidity, but that is why you use a rusting box with either a hot plate to keep the water warm or a few light bulbs to help bring the humidity up.

As suggested, give him the work that he does well, chokes.

David