Hello Milos...

Just about any brand of mineral oil will do.  We can get it at our local
pharmacies, but then it would depend on what similar type of stores you have
in Yugoslavia.  Usually mixing it half and half with mineral spirits
(yes...there are many other things to use!) and brush it on the shells or you
can dip small ones and then set them on paper towel or newspaper to absorb
any excess.  I find it gives the shells a nice "natural" look without making
them shiny.

Happy Shelling

Richard Sedlak, Fort Lauderdale, Florida