OKU Laboratory

How to Cook the Edible Retoreflector

　

This page describes how to cook the edible retroreflector.

 

• Recipe A (reported in VRST 2017 paper, achieved refractive index of ~1.4335)

  • Ingredients

    • Water : Kanten (agar) : Granulated sugar : Glutinous starch syrup = 100.0 : 3.6 : 100.0 : 8.0 (weight ratio)

  • Directions

    1. Prepare heat-resistant container. Measure its weight if not known. A Pyrex beaker was used in our case.

    2. Add kanten to water and heat them. In our case, a hot plate (NHS-M200ND, Nisshin Rika) with aluminum beads was
       used.

    3. After the kanten has completely dissolved, add granulated sugar little by little. After all of the granulated sugar is dissolved, add glutinous starch syrup and mix. At the initial state, add a little more water than the target amount calculated from the ratio since some water will evaporate during the heating process.

    4. Boil the mixture to maximize the performance of the Kanten until the water weight is reduced to the target weight, and remove the container from the heater. The water weight can be estimated by measuring the total weight.

    5. The boiling process produces many tiny bubbles in the mixture. By letting the container stand for several minutes, these bubbles will rise and the mixture will separate into an upper thin layer of foam and a lower layer of transparent solution. Skim off the upper foam.

    6. Place a corner cube-type retroreflector as a mold on a petri dish and pour the solution into the mold slowly from
       above.

    7. Remove any remaining bubbles by using a pointed stick. Spraying an ethanol solution like food sanitation alcohol helps to remove the bubbles.

    8. Put the petri dish in a refrigerator to cool down. After the mixture has coagulated, remove it from the mold. Sometimes,
       the coagulated Kanten sticks to the mold and is very hard to remove. To prevent this, wrap the petri dish with a wet dishcloth during cooling. In our experience, the sticking seemed to be caused by desiccation in the refrigerator.

 

• Recipe B (higher refractive index of ~1.4730 can be achieved)

  • Ingredients

    • Water : Kanten (Karikorikan, Ina Food Industry Co., Ltd.) : Granuated Sugar = 120 : 5 : 250 (weight ratio)

  • Directions are almost same as in the recipe A, but you don't need to add Glutinous starch syrup which is only used in the recipe A.