The oil cup should always have the cover on except when taking oil from it. Before it is refilled it should be very carefully cleaned.
The oiler should be perfectly clean, that kind which has a hexagonal nut on the handle and a gold tip being very excellent. Some careless workmen wipe the oiler on the back of the hand, on the clothes, on a dirty rag, on an old chamois, etc. The tip of the oiler should never touch the hand or fingers, as the acids in the perspiration are sure to cause a bad effect on the oil.
The following is a list of "oilers" which the author has seen used:--Peg wood, broom straw, quill, toothpick, match-stick, screw driver, tweezers, rat-tail file, piece of copper wire, horse-shoe nail, steel pen.
If dust be on the bench paper, or in the movement tray, the pivots will surely transfer some of it to the bearings when the wheels are being put to place.
The scape-wheel, mainspring and other parts, the rubbing surfaces of which may come in contact with the fingers, should be so handled as to allow no perspiration to become deposited on any surface which may afterwards require oiling, as the acids contained in the perspiration will exert an injurious effect on the oil.
The owners of watches sometimes subject them to very hard treatment by using perfumes, etc., and then some people perspire more than others, while the perspiration of some persons contains more acids, or is more rancid, than that of others. For these reasons the method of testing oil by putting it on watches kept to loan to customers as Saunier recommends cannot be relied on.
Oils should be kept in a clean, cool, dark place. The wrapper or label on the bottle should be dark blue or black, to exclude all light, as, if this is not done, the oil will be more liable to decomposition, except in the case of a mineral oil, which is not affected by light. All vegetable and animal oil which has been "bleached" by exposure to the light is more liable to decomposition on exposure to air than that which is unbleached.
~88. The Effect of Age on Oils.~ Writing on this subject Mr. Henry G. Abbott[28] states as follows: "There is a popular fallacy existing in the trade that oils should be used when fresh, and even that acknowledged authority, Saunier, says, 'do not buy from motives of economy bottles that have laid for years in the shop.' This may be true and probably is in regard to animal and vegetable oils, which are likely to become rancid if kept for a long time, but William F. Nye, one of the largest and most celebrated manufacturers of fine watch and chronometer oils in the world, declares that blackfish oils are improved by age, and his oils are seldom placed on the market in the same year as obtained. We are indebted to the same authority for the statement that oils of this kind are clearer and more brilliant after some years than fresh oils." Though Mr. Abbott has made some very valuable additions to the literature of the profession, the author begs permission to call attention, in reference to this, to the following facts: