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 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.
Keep in mind that amber has a density that is lower than that of glycerin, so it floats in this liquid. It is therefore necessary to fix the sample with plasticine (for example) on the bottom of the container and let the liquid flow until the sample is completely covered.
Caution should be exercised when pouring the glycerin because air bubbles may form between the bottom surface of the amber and the glass container; these are difficult to remove once formed. It is consequently necessary to remove the amber, dry it and use a new container.
Sometimes air bubbles may also form on the surface of amber, which should be removed with a needle and by using a stereomicroscope.
A recurring problem after multiple acquisitions have been made in glycerin is the presence of inclusions that float or move freely in the liquid. These are synthetic fibers that are present in the air or left behind by the fabrics used to dry the glassware or dropped accidentally. The slow movement is recorded in the frames you take, and the result often risks compromising the final photograph. In the example below, a beautiful (and rare) scorpion is “photobombed” by a hair that slowly and quietly crosses the field of view, leaving an irreparable trace that is impossible to remove.
This is an extreme (but not rare) case, but the judicious use of the tools available in Adobe Photoshop helps to resolve these unpleasant effects in many cases.
But what is the difference between an acquisition without and with glycerine?
In the two images below, you see a photo of a subject that is closer to the edge of amber with a hemispherical surface (worst condition to obtain good images). I have used both images in 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 insect.
The final image after processing.