For Christmas 2022 I got some Diamine 'gold star' fountain pen ink, it comes in a cool bottle in the shape of an eight-pointed star:
The ink is a orange-gold colour, but the most interesting property is that it is a 'shimmer ink', that is it reflects light back from glitter-like particles that are suspended in the ink.
I was curious what the reflective particles looked like under the microscope, so I pipetted 10 μl onto a microscope slide and covered with a coverslip.
I have quite a nice Nikon microscope that can take good pictures. This image is with the low power 10X objective and shows numbers particles that are quite irregular in shape. The scale bar in the image is 100 μm or 1/10 of a millimeter (about 4 thousandths of an inch). most of the particles are much smaller than this length.
This next image is using the 40X objective with differential interference contrast, and is a composite image of 6 slices though the Z-plane. This time the scale bar is 10 μm. This image really shows the irregular shapes and sizes of the flat particles, and even their irregular surface texture.
I am not sure what the particles are made from, perhaps a mineral like mica?