A practical approach is a low-magnification dissecting (stereo) microscope rather than a high-power compound microscope. For particles in the 0.05–0.1 mm range, a dissecting microscope can give you useful magnification while providing much more working distance and depth of field, which matters when the particle is embedded inside 6 mm-thick glass.

For imaging, you can attach a DSLR or similar camera to the microscope using a microscope-to-camera adapter; these commonly replace the eyepiece or connect through the microscope’s photo port.

Lighting is critical. Instead of only front-lighting the sample, illuminate the edges of the glass so the glass acts like a light pipe and carries light to the embedded particle. Lighting from multiple edges can help reveal surface texture and improve contrast. Keep the background dark to increase visibility, especially for light or translucent particles.

So the key setup is: stereo/dissecting microscope + camera adapter + careful edge lighting of the glass.