Bay © Sesh “Aprit 5, 1872. The 1st offset = R— 7 R?— 1 The 2nd offset = R— Y R2— 4 The 3rd offset = R— V7 R?— 9 The 4th offset = R — V R? — 16 The 5th offset = R — 7 R2—25 Now, R — V7 R?—- T= T2 T! ZR T SRY and in setting out curves of small radii from the tangent line, these corrections need to be made, but for curves in use on railways the quantity
TT 8 R8 is too small tc affect the result in practice ; therefore we may take
72 2R To find the direction of a new tangent, let cd (Fig. 2) be the last offset on the tangent line ac, and it is required to determine the direction of the new tangent )f Take
bd=ab. Let the distance ac = 'T,ab =2,
and cd = O. Then2?= (T — xz)? + O07,
oe 0: iz 0
Misa @2 a 3).
Se ey) 7 aaa
Therefore, to half the length of the tangent,
add the square of the last offset divided by
twice the length of the tangent, which will
give the distance of 6 from a; range the line
b f through d, and proceed from d as before.
The land-measuring chain (Gunter’s), of
66ft. in length, divided into 100 links of
7-92in. each, has been commonly used for
setting out railway curves, although the
100ft. chain is preferable ; but when the 66ft.
chain is used, the rule becomes for offsets in
feet—
O= = X 66, or = x 33 = offset in feet.
Another method of setting out curves by
offsets is the following :—If ab (Fig. 3) be
a tangent to the curve at the point a (= T),
find the first point in the curve at cas before,
by laying off the offset 6 ¢ (= VU), according
to the formula
2
28
Range a line from a through c to d, and make
c d (say) = 1 chain, and ce equal to it. The
offset
dea al x cle RR Range now a line from c through e to f, mak- ingef=ce; chaineg = ef; the offset fg= cies mi and so on. These are elementary methods of setting out curves where the ground is clear, but many curves in practice can only be set out with the theodolite by means of angles; but to follow out these more recondite methods would lead us too far from our subject. Stakes having been driven at intervals along the centre line, the ground is nicked out between them, the nick being cut 6in. wide at the top and 4in. deep. ——_—__—_ DECORATIVE PROCESSES. GRAINING, STAINING, AND INLAYING OF MARBLES. By an ExpreriencepD WorkMAN. (Continued from page 251.) Ts our last we described the system by which we imitate crayon or veined marbles in contradistinction to those marbles in which the crayon is very rarely if at all used : as a representation of this class of marbles we may take Rouge Roi; as an illus- tration of our methods of imitating them, Rouge Flenri, Rouge Jasper, S. Remy Blue, Saracalin, Brocatellas, in part on the same system and part crayon. Lapis Lazuli and
THE BUILDING NEWS. 271
others may be done on this system, allowing, of course, for the difference in colour and character. These marbles seem all to have one particular characteristic feature which indicates that at one time the whole of their component parts have been in a fluid or semi-fluid state, and in this state to have flowed the coloured matter on to the white and gray spar like lava from the yoleano, and thus the variation in colour and form has been produced, and thus also we may account for the absence of veins or dividing lines by which crayon or veined marbles are distinguished. Rouge Roi—Our system of painting this marble, which, as we have before said, will serve torepresent a class of marbles capable of being imitated in the same manner, is as follows :— We paint the ground-colour white or light gray, stippled in flat colour. We now mix boiled oil and turps together, adding a little japanner’s gold-size to dry and set it. Mix Indian red and burnt Oxford ochre in a stiff paste, making a light red of a yellowish tone. Mixalsoadarkerred with Indian red and drop black, also a strong blue gray, and another of Indian redand burnt Sienna; use a stiff brush, and rub over the panel to be marbled with the oil, turps, and gold-size. Now take a little of the light red and cover over the whole of the panel with this, adding a little pure Oxford ochre here and there, then cover a portion with the darker red. When this is done, we take a piece of stiffish paper and crumple or roughly fold it into a broken ir- regular form ; we dip this into turps, then into the blue gray, and dab the work over with this somewhat irregularly, same as the real marble, and using a piece of rag to dab after the turps and blue; this will prevent the turps and blue running, take off any super- fluous colour, and break up the whole. We also use a clean piece of stiff brown paper crumpled up, and press this on to the work, giving it a slight twist while in con- tact with the paint. This breaks up the ground, and shows the white or gray ground through the red, with a beautiful effect. We now take a flat tin tool, or a large swan quill pencil, and turps, and with this we open out the large patches of blue, gray, and white in this wise: we dip the pencil into the turps, then slightly into the blue, gray, and black ; we then roughly form the patch we want, and then dab with a clean rag, which prevents the turps running, and produces the effect we require. In fact, the latter method puts in all the under work, and helps to give that depth and transparency seen in the real marble. Of course this description will be best understood if we have a specimen of the marble described before us. We now use clean turps and paper, dab it on to any part we wish to be lightest, and gently use a clean rag to wipe out the light parts or solid whites. A little pure black in oil, put on with the paper before commencing the dabbing with the rag and turps, adds very materially to the effect in the darker parts of this marble ; and if the paper is crumpled or folded pro- perly, certain accidental forms and figures will be formed, very like the markings in the marble, which it would be difficult, if not al- together impossible, to get with the pencil, except by an immensity of labour, The work is now allowed to dry, and is then ready for glazing and finishing. We now mix a little flake white, thin with turps, and add a little ultramarine blue, but only suffi- cient to give it slight tinge, something like the transparent white spar parts of the marble; with this, which must be used thin, we put on a white or gray vein or patch, and while it is wet we put on the centre, or one side, a streak or patch of solid flake white, and then gently soften or blend the one into the other, but only just sufficient to cause the solid parts to graduate into the thin transparent white previously put on. If thisis done carefully the effect will be all that can be desired; in this way we go over the whole of the white and gray parts, using darker gray and blue, and some-
times a little black to give depth and shade.
We may now scumble a little thin white here
and there over the surface with a feather.
We now mix two or three shades of brown
or red, as near the colours of the reds or
browns in the real marble as we can, and with
a tin tool and swan quill proceed to put in
the patches of red and brown, cutting into
the whites and grays and bringing them into
form. This must be carefully and judiciously
done, and while it is wet; clean crumpled
paper may be used to partially break up and
give depth to the solid patches of brown and
red. By this method we get precisely the
effect of the real marble—the dark parts,
which are principally red, seem to flow upon
the gray and white, and give depth and
transparency by making them appear as if
they were underneath. When this is dry we
may again touch up the whites, and glaze the
dark parts to enrich it. Some persons try to
imitate this marble by painting in the ground
a dark red, and when dry putting in the
whites and grays upon the top; but it will
be at once evident that we cannot get that
depth and transparency so necessary and so
characteristic of the marble, and so simply
effected by our own system.
Feather marbles, or marbles which are
imitated principally by the use of the feather,
are, as a rule, all green marbles, and in some
of these both the sponge and feather may be
used with advantage. The middle-sized
feathers of a goose’s wing are the best for
our purpose—neither the largest nor the
smallest are of much use, although there
is one feather on each wing which is so
beautifully formed and so firm, and has so
fine a point that it may be used as a pencil,
and a beautifully fine line may be run with
it. This feather may be found close to and on
the top part of the large bone of each wing,
buried under several large and smal! feathers,
We have no doubt but that this feather was
known and used as a pencil by most savage
tribes for painting fine lines and streaks on
their persons. Kgyptian Green, Vert des
Alpes, Verd Antique, and some few other
marbles may be done on this system. ‘There
are two methods of imitating these marbles.
The first is as follows :—The work is painted
a dead black ; we then mix a few shades of
green, from a dark green to a light tint, just
removed from the white. These colours are
thinned with turps, so that they will work
free, anda little japanner’s gold size is added
to cause them to set in use. We dip a feather
into the darkest green, and lightly feather or
streak over the whole of the slab with it,
leaving spaces uncovered. We next go over
the same ground with the next lightest green,
and so on with the various shades of green ;
and if we then use a thin white and the
feather, and slightly blend with the badger-
hair softener while it is wet, a capital effect
may be obtained. We may now use a pencil
or swan quill, and put in the strong light or
white veins; when this is dry, we may add
very much to the richness and depth, or trans-
parency, of the marble by brushing over the
whole of the slab with a thin glaze of trans-
parent green (yellow lake and Antwerp blue
will produce a brilliant transparent glaze) ;
or we may use a glaze of permanent green,
and while this is wet we touch upand heighten
the whites, which will give an excellent effect.
The second method of working is by having
the ground colour white instead of black ;
the greens are put on the work, and it is then
feathered with turpentine, and streaked by
removing the colour instead of putting it on,
as in the first system, the whole being
glazed and touched up afterwards. This
is a capital plan for doing Irish Green,
or Irish Serpentine, but is notso good for other
green marbles.
Several of the green marbles may have the
first two or three shades of green put in with
the sponge, and then finished with the feather,
by which meansa capital effect may be obtained.
The sponges required for this purpose, and
for imitating the various kinds of granite and
