The image presents air bubbles created in melted and then dried polyvinyl alcohol. Magnification 100X, technique of the illumination is dark field and polarization.
<a href="//commons.wikimedia.org/wiki/User:MarekMi%C5%9B" title="User:MarekMiś">MarekMiś</a>
CC BY 4.0
<span class="int-own-work" lang="en">Own work</span>