Practically "permanent" slides can be made with the aquous medium  Starmount (www.biochemreactives.com or www.planktoniclife.com).Although actually I am retired,  I use it every day for routine work with marine plankton (including polychaete larvae) and the results are excellent. I have preparations made four or five years ago. The refraction index is high (1.53). If the slide must be transported inmediatly or its content is specilly important I should recommend sealing the coverglass borders with transparent nail polish. This mounting medium  is quite cheap, about 0.10-0.20 € / preparation. Important: the amount of water in the specimens must be removed at maximum (with filter paper on one or two sides), to avoid dilution of mounting medium.

Semipermanent slides can be made with a mounting medium of 30% glycerol and 70% Polyvinyl alcohol-based clear glue. Elmer's or Colorations are good sources of clear glue. Use a lot because about half of it is water, which evaporates. It will last as long as the glycerol does not evaporate, which is years. To prevent glycerol-based mountants from evaporating, place an open dish of glycerol in the slide cabinet to keep the air saturated with glycerol.

We have long used Gurr Aquamount for semi-permanent slides and, after setting, seal the edges of the coverslips with clear nail varnish. Can't seem to find it on the internet, so it may no longer exist.  I have, however, came across this post (http://www.histosearch.com/histonet/Dec99/RE.Aqueousmountingmedium.html) suggesting Dako Faramount.  The initial post indicated that Aquamount can easily incorporate bubbles, and we have found this also. Unfortunately, I have no experience with Faramount and it seems much more expensive than I remember Aquamount was (http://www.agilent.com/store/en_US/Prod-S302580-2/S302580-2?navAction=push&catId=SubCat3ECS_86669&pCatName=Mounting%20Media&navCount=0).

Thank you Richard and Andy for your answers. Faramount sounds good, but as you said Andy, is quite expensive. Maybe there is another similar substance that is cheaper

Practically "permanent" slides can be made with the aquous medium  Starmount (www.biochemreactives.com or www.planktoniclife.com).Although actually I am retired,  I use it every day for routine work with marine plankton (including polychaete larvae) and the results are excellent. I have preparations made four or five years ago. The refraction index is high (1.53). If the slide must be transported inmediatly or its content is specilly important I should recommend sealing the coverglass borders with transparent nail polish. This mounting medium  is quite cheap, about 0.10-0.20 € / preparation. Important: the amount of water in the specimens must be removed at maximum (with filter paper on one or two sides), to avoid dilution of mounting medium.

Thank you Antonio, Starmount sounds quite well. I guess if the sample is very small (for example, a single parapodium of a polychaete) there's no need to dehydrate it (it would be very difficult to perform even with filter paper) as the amount of water it contains i s low

Of course Diego, Always the minimum amount of liquid and well mixed with the mounting medium, I use Starmount for preparation  of a single appendage of a copepod crustacean.

Thanks Antonio.  Starmount looks a good option, and not too expensive

I often use Euparal, which is also not so expensive.

Euparal is cheap, but Starmount works better.

In 30 years of fiddling with mounting media, I have never found a luting agent (sealing the cover slip) that worked. Sure, among a hundred slide one may be sealed after 10 years, but glycerine, which is the only non-poisonous liquid high boiling point mountant, will eventually evaporate. No mount that is not perfectly solid will not evaporate given time. Putting your glycerine mount slides in a cabinet with a dish of exposed glycerine will retard evaporation. NOT sealing a slide is best, because then you can lever the cover slip off easily and add more mountaint if needed.