This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
In every case in which steam is used at a pressure exceeding that of the atmosphere, either as a motive power or a heating agent, it is necessary to make the machinery or piping connected therewith in many pieces, for obvious reasons, the chief of which is convenience in manufacture, and wherever these are joined together to hold or convey steam it is necessary to make the joints steamtight. For this purpose there are almost innumerable methods, but we only intend giving briefly a few notes on those in which red lead is used, which are most familiar to those connected with the trade of an engineer; but notwithstanding this familiarity, nineteen out of twenty mechanics have very erroneous ideas on the subject, and consequently many joints are the cause of much delay, trouble, and expense, which could easily have been avoided if the general principles were understood. The fundamental principle of all joint-making is, that the thinner the joint the stronger and more durable it is.
Each face must have all the old lead removed, and then be wiped over with a piece of oily waste (boiled linseed oil). The lead must be thoroughly worked, either by machine or by hand, to make it soft and pliable, and also to remove all grit and lumps. It should then be rolled in the hands into thin ropes, about 1/4 in. diameter, and laid on once round inside the bolt holes. The 2 faces must now be brought together carefully, and tightened up equally all round, by screwing up opposite bolts, so as to avoid getting one side closer than another. Tarred twine, hemp, string, wire gauze, etc, should be studiously avoided wherever possible, as it prevents the faces from being brought into close contact. There are certain rough jobs where it may bo permitted, but a joint so made is never so durable, and very clumsy. When joints are accurately faced, by scraping or otherwise, as in locomotive practice, nothing but liquid red lead is used, made of white lead mixed with boiled oil to the consistency of paint; they are of exceptional durability.
(b) Joints between male and female threads, such as screwed pipes and sockets, bolts or studs screwed into boiler plates, etc. - In these cases liquid red lead is used, and should be put on the female thread for inside pressure, on the male for outside pressure, as then the steam in each case forces any surplus lead into the thread, and forma a more reliable joint, or rather assists it; whereas, when it is applied in the reverse way, as generally done, the threads are left quite bare and clear, leaving nothing to assist the joint.
These methods, broadly speaking, apply just the same to the various compositions sold as substitutes for lead, the chief advantages claimed for them being cheapness and durability; but they can never surpass, or even equal it, if it be only used as explained, especially if a little common sense be applied in special cases.