In the case of a gel made from 1 % gelatine in water, we estimate that the index would be similar
to the one of a solution distilled water, in the standard conditions of temperature and pressure.
n gel = n water = 1, 33335 (x; precision 10-5).
Figure 10: Example of a succession of reflections and
refractions on a glass prism.
Figures 11 and 12:
Example of waves guide,
monochromatic light ray through a
15 / 63
calculation of the critical incidence angle:
n gel = n water = 1 ,33335
n air = 1.
qi = arcsin (n gel / n air) = 48, 59 °.
III.4.3. First test of a wave guide.
· Stamps in stainless steel with parallelepipedal shape (8 x 4 x 4 cm).
· Gelatine leaves supplied by Louis Francois
· Agar-agar supplied by Louis Francois.
· Plastics tubs.
· Cartboard and aluminium foil.
Two tests are done, one with some gelatine, one with some agar agar.
1. Make cardboard cylindrical stamp (length = 8 cm, diameter = 1,5 cm) and cover it with aluminium.
2. Make a solution of gelatine or agar agar at 1.2 %.
3. Poor this solution in the parallelepipedal stamp where the cylindrical stamp is placed.
4. Place the mould in the frigde and wait for gel formation.
5. Turn the gel out of the tin.
Figure 13 : 1er test with agar-agar at 1%
III.4.3.4. Discussion/ Interpretation:
The two different gels set properly at 12 g /l, but with gelatine, it is not easily manipulated as it
breaks easily. Thus, the gelatine won’t be used anymore.
Also, the stamp is too big to be used in the restaurant. It is necessary to reduce its dimensions
and a new test is realized with a smaller stamp (3 x 3 x 7 cm).
The technique however works, as we observe a concentration of the light on the internal cylinder.
III.4.4. Smaller stamps.
III.4.4.1. Material and method:
The same method is used that in III.4.3.1. with smaller shapes.
The gels are realized with agar-agar according to various concentration: 0.5 %, 1 % and 2 % to
determine the best texture given by the concentration.
The solution is put in the parallelepipedal stamp and when the gel is set, the guide of waves is