Begin by creating a drawing or using a small picture (depending on the context of the trick, in the following video are several examples).

Insert the drawing into the plastic bag, ensuring that it is fully sealed inside. Draw or write with an acetate pen what you want to see when you submerge the plastic bag in water.

Fill a container with Water.

Submerge the Bag in Water.

Observe the Illusion: As you lower the bag into the water, you will notice that the drawing seems to disappear and we can only see what has been drawn or written in acetate pen.

The trick involve a simple optical illusion that demonstrates the concept of total internal reflection.

The illusion occurs due to a phenomenon called total internal reflection. When light travels from a denser medium (in this case water) to a less dense medium (in this case the air inside the plastic bag), the light can undergo reflection at the boundary between the two mediums. However, if the angle at which the light strikes the boundary is too shallow, the light does not escape but reflects entirely back into the denser medium.

In this trick, the plastic bag acts as a boundary between the water and the air inside the plastic bag. When you submerge the bag in water, light from the drawing inside the bag encounters the bag's surface at a shallow angle. Due to total internal reflection, most of the light reflects back into the water, making it difficult to see the drawing clearly.

It gives the impression that the drawing on the inside of the bag has disappeared. 

Idea: This illusion can be performed with children to demonstrate the importance of hand washing.

You can also use 2 plastic cups: