Clear or Opaque?

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Author: Beth Gilbert

Being clear can be defined as a quality or purity, and at other times we need to make a substance clear such as glass or varnish. Opaque can be defined as neither transparent nor translucent.  If we have a better understanding of clear vs. opaque then we can achieve the ability to convert opaque materials to clear materials or clear materials to opaque. We all have seen glass/plastic, soaps and shampoos, and certain foods, in clear conditions, and have seen the same things in opaque (not clear) conditions. We will find out how being opaque or clear is an optical property.


Why some materials are clear and others are opaque?


  • Salt
  • Sugar
  • Ice cube
  • Hammer
  • Dish towel
  • Plastic baggie
  • Pen and paper
  • Camera (optional)



  1. Gather the salt crystals. Take one salt crystal and lay on a flat surface (kitchen counter/kitchen table) Look at the salt crystal. It should be clear. Document what you see
  2. Take a spoon full of salt crystals and put them on the same flat surface. Look them all together.  They should be opaque even though it is many clear crystals together. Document what you see.
  3. So far we know that crystals are only clear if they are in one piece.
  4. Repeat steps 1 through 4 with sugar this time. Document what you see.
  5. Next, take an ice cube and look at it on the same flat surface. It is clear.
  6. Put the ice cute in a baggy, cover with a dish towel, and crush it with the hammer.
  7. Look at the crushed ice cube. In pieces, it is no longer clear, but is now opaque. Document what you see.
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