I have a Condit Pin Registered Oil Immersion Carrier. Robert Pace who is one of the world's premier photographic printers recommends oil immersion.. to reduce refraction from the carrier glass... along with a point light source. There are other fluids that are usable including turpentine. Oil immersion is also used with microscopy.
The media Bob Pace advises using is Dow Corning fluid 200 viscosity 100. He recommends cleaning the oil from the negative or positive with a three successive dips ito three different containers of film cleaner amd then hanging the film chip to dry.
I am going to make a suggesstion here:
Get hold of some glass slide mounts w/o anti-newton glass. Use these for your carrier. If kami fluid is being used you may have to seal the slide mount to prevent evaporation of the fluid. When using oil bubbles are a real PAIN IN THE ASS. You have to get the bubbles out of your image area. I suggest that you work on a level surface and that your enlarger holds the carrier in a level plane. I am not talking about alignment here..If you eliminate the bubbles when on a level plane and then insert the carrier into a properly aligned enlarger that is NOT level the bubbles will drift. If you wish to see just how fine of a circle your enlarging lens can project then having bubbles in the image area will illustrate it for you nicely My lawd what clear and tiny bubbles you will project....perfection indeed!
Along with preventing refraction from the carrier glass scratches and transparent dust motes will disappear.