Account of the Skerryvore lighthouse

by Alan Stevenson

As a conclusion to the above account of quarrying, it may perhaps be thought desirable to give some notion of the probable time required to perform certain parts of that sort of work. In boring holes of 1 inch to 1¹⁄₄ inch in diameter, it may be observed that they are generally done with the hand mall ([fig. No. 14]), one and the same person striking with the mall with one hand, and turning the boring tool for himself with the other; and in most cases a man will bore 9 or 10 inches an hour in granite rock. If the bore be 1¹⁄₂ inch diameter, as for plugs, three men will generally bore two plug holes in one hour, each hole being about 9 inches deep. If the bore be for blasting and of 2 or 2¹⁄₂ inches diameter, three men will bore, at the rate of one foot per hour, to the depth of 6 or 7 feet; but if the bore be for a large blast of 13 or 14 feet deep, the hole must be 3¹⁄₂ inches in diameter at the top (diminishing to 2³⁄₄ inches at bottom), and will employ three men working hard between two and three days. Bores of that sort, indeed, cannot be made (at least by hand) to a greater depth than 14 or 15 feet, as the weight of a rod of iron, 17 feet in length, and 2 inches in diameter, makes it quite unmanageable for one man either to turn or to lift; while, from its great mass, the strokes of the mall produce little effect on it. The malls used in boring holes, which require three men, are 7 or 8 lb. weight, having handles 3 feet long (fig. No. 15), and are swung over the shoulder, while striking for down bores, in the same manner as a smith’s forehammer is used. An expert cutter with the wedges will make good wages by cutting holes at the rate of 2¹⁄₂d. for a dozen of holes, taking light and heavy cuts as they come to hand.

No. 15.

What has been said above of boring and blasting refers only to downright or vertical bores; but, in the lower parts of a quarry, it is often necessary to have recourse to what are called breast-bores, from their running in a nearly horizontal direction and piercing the front or breast of the rock. Those bores are not so easily made as the downright bores and, in general, are only used where the rock is low, or in taking up bottom rock. They can seldom be carried to a greater depth than about 9 or 10 feet, owing to the difficulty of turning the jumper, and can never be bored quite horizontally, but require as much dip as will retain a little water in the hole to keep the jumper moving. Instead of throwing the mass outward, as is done by down-bores, those breast-bores generally only cut or break the stone in the direction or line of the bore, so that the block always requires to be afterwards removed by bulling, in the manner already described.

Dressing of the Lighthouse blocks. The dressing of the blocks for the Lighthouse Tower, as already mentioned, was one of the most important operations in the workyard at Hynish; and as no writer with whom I am acquainted has given any account of the mode now practised of dressing granite, I hope I shall be excused for attempting, in this place, to give some idea of the method employed by the masons of Aberdeenshire, whose skill in that department of workmanship is well known both in our own and in other countries. As the whole of the materials for the Tower were to be dressed in such a manner as to avoid the necessity of any fitting on the Rock, by the introduction of what are technically called closers, the greatest accuracy in the formation of the moulds from which the stones were to be shaped became necessary. With that view, I had a trainer or radius made with a moveable vernier, capable of sliding along it, so as to give the differences between the readings of the feet, as far as to the thirtieth part of an inch; and I was thus enabled to lay off the batter or slope on each course (according to the quantities in the [Table of Co-ordinates] in the [Appendix]) with great nicety, and so to trace very distinctly the contour of the intended column.[22] On the stone floor of an apartment in one of the workshops, the quadrant of each course of the building was carefully drawn out, at full size, and divided into the sectors which were required for preserving a due bond among the joints of the adjoining courses. The form of each stone in the tower having been thus determined by those full-sized draughts, moulds, representing the beds and sides of each stone, were prepared according to them, of seasoned timber, well shielded at the angles with sheet-iron, to prevent their being injured. Those moulds having been marked with reference to the number of the course, and the position of the stones in the wall, were given to the foreman of the workyard, who regulated the work of each of the stone-cutters, often to the number of 70 men. A proper block having been selected for each stone, leaving about 1¹⁄₂ inch all round the extremity of the moulds when applied to its several faces, it was conveyed, by means of the sling-cart, to the shed where it was to be dressed. The shed for dressing granite stones differs in no respect from an ordinary mason’s shed, except in its greater height; but, as the stone cutter, in order to wield his tools to advantage, must, at certain parts of the work, stand on the top of the block, it has been found, that a height of about 15 feet is required for the back-wall of a granite mason’s shed. Each man also requires, for large blocks, a space of about 10 feet (measured along the front of the shed), as his peculiar territory.

[22] Such nicety, I would observe, was by no means superfluous, because the arrangements of the Tower precluded the possibility of using a trainer in building; and as the whole was done by means of plumb-templets, the greatest accuracy in tracing the curve of the Tower became necessary, as the only true basis of good workmanship on the Rock.

When a block has been brought to the shed, the first thing to be done, if it is a large stone of 1¹⁄₂ or 2 tons weight, is to lay it nearly level on the ground, with the side which is to be first dressed uppermost. The form or plan is then sketched upon it according to the mould, and the stone is blocked out with a large hammer weighing 30 or 35 lb. ([fig. No. 16]), which is the most suitable weight for ordinary men, although a stout man will manage one of 40 lb. well enough, if the block be lying in an advantageous position. When the stone has been thus rudely blocked out, it is set upon its edge with a gentle inclination to one side, so that the mason, who mounts on the top of it, may conveniently use a pick of 18 lb. weight, having a handle three feet long, to dress off very roughly the most prominent parts of its irregular surface. In doing that he makes a great many deep ruts in a downward direction, at the same time taking care that none of them shall be so deep as to fall below the general surface of the stone when finished. When he has in that style dressed as far down the surface of the stone as he can conveniently reach, (and that is generally about half way,) the stone is then thrown over and set up on the opposite edge, when he again mounts upon it, and goes over the rest of the surface in the same manner, until the whole shall be reduced to one rough plane, so that in spite of numerous partial inequalities, the general face may be straight, or what is technically termed out of winding. A stone in that state is also said to be well opened.

No. 16.

No. 17.