Many people asked me what technique I am using to photograph insects in ambers. The inspiration comes from Hellberg Jörgen, a Swedish photographer who on his website https://www.hellberg.photo/ describes the different results of photographing an amber with and without immersing it in a liquid.
The results are amazing!
The surface of an amber is rarely perfectly flat and parallel to the subject you want to capture. Instead, it appears generally irregular or curved and, worse, it happens that the insect is closer to the lateral edge. This causes optical deformations when stacking the images, such as reflections on the surface, visibility of scratches, flaws and fractures affecting the quality of the final image.
A method to obtain neat images and to make almost perfect results, is to put the amber in a transparent or semi-transparent container (to facilitate the diffusion of light) and immerse it in a liquid that has approximately the same refractive index.
The best solution is to use glycerin. The refractive index of this liquid is 1.472, while that of amber is about 1.54; the very close values of the two substances make it possible to minimize the phenomena of light diffraction, hide the majority of scratches and fractures, and create the best working conditions for obtaining correct images. In the absence of glycerin (and cheaper solution), sunflower oil can also be used, which has a refractive index between 1.472 and 1.476. You can also use immersion oil for microscopy (refractive index of 1.516, even closer to that of amber), but the price of the latter and the need to use a relatively important quantity (depending also on the size of the amber), makes this technique relatively expensive. Finally, the use of a polarizer can help to eliminate any reflections present on the surface.
In the two images below, you see a photo of a subject that is closer to the edge of an amber with a hemispherical surface (worst condition to obtain good images). I have used for both images the same lighting conditions and no corrections have been applied to improve the contrast, the sharpness, to eliminate the noise, and remove the defects present on the surface.
Subject without immersion in glycerin:
In addition to the poor image quality obtained (A), you can observe the deformation to which the insect is subjected when closer to the edge (B); a bright surface on the right side is the result of the reflection of the light coming from the LED panel, despite the presence of a diffuser (C); scratches, indicated by red arrows, are clearly perceptible on the surface (D); the details are lost near the outer edge (E).
Below is the subject immersed in glycerin:
The difference between the two results is even more visible by zooming in on the head, and observing the details of the composite eyes, as visible in the inset.
The final image after processing.