In this case, we make a biconvex lens.
To do this, we cut out two convex blanks of the same shape from the “shoulder girdle” of the bottle. These blanks need to be glued together with clay, chewing gum or clay .. It is better to use the first 2 materials for bonding :-).
After bonding, it is necessary to completely fill with water (without bubbles) the entire internal volume of the future lens.
It is better to fill the lens with water as shown in the figure. After filling the lens, it is sealed on all sides so that it does not leak or pass air inside.
All the lens is ready. You can unload small text, work with small objects and make a fire.
Source: sdelay-sam.su
