> How you see if your mix has the same refractive index as the glass I haven't figured out yet.

You can do this by direct observation but it is not going to be 100% accurate:

You'd need some kind of etched grating for reference.

Drop the glass+grating into the mix, check for changes to the grid lines where you know the glass resides. If you can spot it then you still have a difference.

You could also simply measure the refractive indices of both. (For most microscopy glass you can find out the exact index of refraction from the manufacturer so you really only need to measure one.)