JMH yes it is the same bluing mixture on that page but also on page 73 "Old English blue" also known as "American trade Express Browne" this is just another variation of the mix. This high Mercuric Chloride formulation was very popular and used by many Birmingham trade barrel finishers in past times. There are many reasons for this but two main reasons where one you could from start to finish rust bluing a set of shotgun barrels in less than an hour. Two you could re-blue worn blue barrel sections without completely re-finishing all the barrel set as long as the original bluing was rust based.
Yes it has high Mercury levels though simple precautions will keep its detrimental effects to a minimum. Working under cover outside of a building is the safest when bluing with this type of express rust bluing method, or alternatively having a high level of air extraction from the work place.
I have used both methods to keep the mercury vapours down to an acceptable safe level, And at 70 I am not as mad as a hatter though the lady I live with may want to say a word or two about that! Though in my defence I would say it is the Mercury Amalgam teeth fillings I have been carrying around for more years than I care to remember.
