Method of producing a bas-relief with a motif which varies with light and the bas-relief thus obtained

A method of producing a bas-relief with a motif which varies with the light, characterized in that the original motif to be reproduced is divided into a grid. The intensity of the grey in each of the divisions of the grid is measured. A numerical value is assigned to each division. The numerical value represents an intensity of grey and corresponds to an element of the bas-relief. The elements of the bas-relief, in accordance with the way in which the grid is divided, are placed side by side in a manner such that the light rays simultaneously make surface shadow spots appear on each element of the bas-relief in accordance with the intensity of the grey of the original motif. The composition of the spots is seen by viewing the bas-relief from a distance and reproduces the original motif.

The present invention relates to a method of producing a bas-relief with a 
motif which varies with the light and the bas-relief thus obtained. 
More particularly, this bas-relief is produced from elements consisting of 
solids with a plane front face comrising a cavity in the form of a notch; 
its illumination by incident light enables illuminated areas and shadow 
areas to be revealed which, suitably delimited, reproduce a motif or a 
defined image. 
Means of producing an image by means of dark spots of variable density on a 
surface area already known: to achieve this; the picture to be reproduced 
is divided into a grid; the intensity of the grey in each division is 
measured and a black spot is made to correspond to this intensity, the 
area of which black spot is proportional to the value measured. These 
black spots of different areas are then arranged on the grid of the 
reproduction, and the basic picture then is found to have been 
reconstituted when it is viewed from a distance. 
The present invention is intended to provide spots by means of the shadow 
produced on an object and to make a motif appear on the bas-relief, in 
particular by means of solar rays, either when the sun is in a defined 
position on its ecliptic or when the ecliptic occupies a defined position. 
It is moreover possible, with the aid of solar light, to make several 
images appear successively with time either on the same day, or on 
different days, on the same bas-relief. 
To this end the invention relates to a method of producing a bas-relief 
with a motif which varies with light, characterized in that the original 
motif to be reproduced is divided into a grid, the intensity of the grey 
in each of the divisions of the grid is measured, a coefficient is applied 
to it corresponding to an element of the bas-relief, the elements of the 
bas-relief, in accordance with the way in which the grid is divided, are 
placed side by side in a manner such that the light rays simultaneously 
make surface shadow spots appear on each element of the bas-relief in 
accordance with the intensity of the grey of the original motif, the 
composition of which spots, seen by viewing the bas-relief from a 
distance, reproduces the original picture. 
Thus, in the case of illumination by the sun, the shadow spots of unequal 
area, but related to the intensity of the desired degree of grey, make the 
image which it is desired to reproduce by viewing the whole from a 
distance, in accordance with the position of the sun on its ecliptic, or 
the position of the ecliptic. 
According to another characteristic, the bas-relief element for applying 
this method, consists of a solid with a plane forward face comprising at 
least one cavity. According to another characteristic, this cavity is in 
the form of a notch and its plane base describes a defined angle with the 
plane forward face of the solid. 
According to another characteristic, the area of the notch, with respect to 
the total plane area of the forward face of the solid, is variable and a 
function of the intensity of the desired degree of grey. 
Thus, the area of the shadow is adjusted in accordance with the intensity 
of the desired degree of grey and by varying the areas, enables areas of a 
lesser or greater darkness to be obtained. In addition the angle between 
the base of a notch and the forward face enables, in the case of solar 
illumination, to delimit the duration of the appearance of the motif. 
According to another characteristic, the bas-relief consists of an assembly 
of side-by-side bas-relief elements, the plane forward faces of the 
different solids being parallel to the same plane, the inclined faces of 
the notches forming a constant angle with this plane, the surface of each 
of the notches being in direct relation with the intensity measured on the 
motif to be reproduced. 
Thus, it is possible to make a defined motif appear, by means of the shadow 
produced on the different notches: the instant of appearance depends of 
course, in the case of solar illumination, on the position of the 
bas-relief with respect to the plane of the ecliptic or with respect to 
the position of the sun on the ecliptic.

The bas-relief with a motif which varies in accordance with the light and 
enables a motif or defined image to appear when it is illuminated by a 
defined incident light is described hereafter, using the sun as a 
particular source of light: the frequency of appearance of the image is 
then a function of the position of the sun and it is for that reason that 
this bas-relief is more particularly called, in this case, a solar 
bas-relief. However, the invention could in no case be limited to the 
utilization of this particular source of light. 
In its apparent movement around the earth, the sun describes a large circle 
of the celestial sphere called the "ecliptic". The angle .phi. of the 
vertical of a location with a plane of the eclipticl varies in accordance 
with the seasons and in particular in the tropics, this angle becomes zero 
once a year, when the sun passes through its zenith (summer solstice). 
For a defined day Jo of the year, the plane of the ecliptic makes an angle 
.phi. with the vertical of a given location: in consequence, if a surface 
is placed parallel to the plane of the ecliptic on that day, all the 
concavities provided on the surface will be in the dark. On the following 
days, as the angle of the plane of the ecliptic and of the vertical of a 
given location diminishes up to the summer solstice, the southern face of 
the surface is in complete shadow. After the summer solstice, the plane of 
the ecliptic progressively approaches the plane of the surface until, 
again, the southern face of the latter is illuminated. 
FIG. 1 represents a wall forming the bas-relief and placed from east to 
west in a substropical region: the plane of the wall and the plane of the 
notch make an angle of 23', an angle which corresponds moreover to the 
average displacement of the plane of the ecliptic in 1 day. 
FIG. 1a represents the position of the sun on the day preceding the 
appearance of the image, the whole of the plane of the wall than being in 
shadow. 
FIG. 1b is the position of the sun the day of the appearance: on that day, 
the plane of the ecliptic is in the angle formed by the plane of the wall 
and the plane forming the notch. Thus, the notch AB is not illuminated, 
whereas the wall is illuminated over all its surface, thus allowing the 
pattern of the notch to appear in the shadow area. As the plane of the 
notch makes an angle of 23' with the plane of the wall, on the following 
day, (FIG. 1c), the plane of the notch is then illuminated for the same 
reason as the plane of the wall and the image has disappeared. Of course, 
the angle .alpha. of the plane of the notch with the plane of the wall 
depends on the duration of the appearance of the image and for a minimum 
duration of a day corresponds to a minimum angle of 23', an angle equal to 
the angle described by the plane of the ecliptic in 1 day. 
The juxtaposition of the shadow spots suitably arranged with respect to one 
another enables an original image to be reproduced at a given instant: 
thus, by dividing the original picture to be reproduced into a grid, by 
measuring the intensity of the grey in each of the divisions of the grid, 
it is possible to make a number representing its degree of grey in each 
case; if now the wall represented in FIG. 1 is made with bricks each with 
a notch whose area is directly proportional to the number representing the 
intensity of the measured degree of grey in the corresponding division, on 
the day of its appearance, the composition of the shadow spots in the 
notches reproduces the original pictures, obtained by viewing at a 
distance from the wall; the wall thus made constitutes what the inventor 
calls a "solar bas-relief", the bricks constituting the elements of this 
bas-relief. 
FIG. 2 represents the elements of the bas-relief in the form of bricks 
entering into the construction of the solar bas-relief. 
The bricks, substantially of parallelepidedic form, have a plane front 
face: this face comprises a notch whose area is variable in accordance 
with the area of the shadow that is desired. 
The plane of the notch makes an angle .alpha. with the plane of the front 
face of the brick, an angle whose value determines the duration of the 
appearance of the image, as has been previously explained. 
The different bricks represented in FIG. 2 each correspond to an intensity 
of grey varying from black to white, the black corresponding to the case 
where the notch represents the entire surface of the brick, the white 
corresponding to the case where the notch is inexistent on the plane 
surface of the brick. The ratio notch area to front face area of the brick 
determines the degree of intensity of the grey and is shown from one to 
six in the example given. 
When the solar bas-relief has been made by suitable assembly of bricks, it 
is then necessary to orient the front plane of their faces to make the 
image appear at the desired instant: thus, this plane must correspond to 
at least one plane of the ecliptic during the year so that the image can 
appear. Thus, if the bas-relief is placed on a tropic, and it is desired 
that the image appear on the summer solstice day, the front face of the 
bricks must be vertical. If the same bas-relief is placed in a subtropical 
region, it can occupy a position slightly inclined toward the north, or 
toward the south, and if it is placed in a temperate region, it must be 
inclined toward the south. In these cases, the appearance of the image 
depends on the height of the sun, that is to say the angle which the 
ecliptic makes with the vertical of a given location and this will occur 
only on one or two defined moments of the year. 
Images can also be made to appear every day, at certain hours: in that 
case, the orientation of the bas-relief is north-south, and does not 
depend on the azimuth of the sun. This bas-relief, in certain cases, can 
be used as a sun dial. 
FIG. 3 represents a variant of the construction of the bricks shown in FIG. 
2: thus, the inclination of the plane of the bas-relief toward the south 
in a temperate region, has a disadvantage insofar as the stability of the 
latter is concerned. However, since the illumination of the front face of 
the bas-relief depends solely on the inclination of the faces of the 
bricks with respect to the plane of the ecliptic, it is possible to make a 
vertical bas-relief, the front face of the bricks then being inclined at 
an angle .phi. with respect to the vertical, the angle .alpha. of the 
notch and the front face being, as before, a function of the desired 
duration of the appearance of the image. This arrangement also has the 
advantage of allowing the appearance of an image on different dates by 
making a bas-relief consisting of bricks having different angles, 
corresponding to the latitude of the ecliptic at various periods of the 
year. 
In addition, by progressively varying the value of the angle .phi. for 
bricks constituting a bas-relief, it is possible to make a linked blend of 
images operating for example from morning to evening. 
According to a variant of the embodiment (see FIG. 4), the shadow area on 
each of the bricks is no longer made by means of a notch, provided inside 
the forward face of the latter, but with a horizontal screen whose 
projection and width are function of the intensity of the degree of grey 
desired. This projection moreover can be made in both cases of bricks 
shown in FIGS. 2 and 3. 
According to another variant of the embodiment (see FIG. 5), the bricks are 
no longer stacked onto one another horizontally, but inclined at 
45.degree. and comprise on each of its two lateral faces projections in 
the form of plates: the plate on the east side gives a shadow on the brick 
during the morning, to give a first image, whilst the sheets, on the edge 
on the west side, give a shadow in the afternoon revealing a second image. 
Of course, the invention is not limited to the examples of its embodiment 
hereinabove described and illustrated, and on the basis of which other 
modes and other forms of embodiment can be envisaged, without departing 
from the scope of the invention.