Hi, I hope I will be able to help you, but you need to write something more about the icon, as I understand this is a hand painted icon, but you don't know what was used to paint the icon... egg tempera maybe? and is covered with varnish? and the gold, it is probably real gold, but just to be sure I ask..
You see without this information it s difficult to say what is safe to use in order to clean the icon..
I would suggest to try to clean with peroxide :take one cotton bud and using hydrogen peroxide slowly and very carefully in one point ( of course not in the middle of the icon) just see if it will do the job. The thing is that if the icon doesn't have varnish you would have to be 100 times more patient
and also in case the gold on your icon is not real then too much hydrogen peroxide and too much power and the gold can stay on the cotton bud
but if it is real gold as i think it is, the things are a little bit easier. You have to know that many old iconographers after putting gold on icon has been "cleaning" gold with cotton with peroxide, because after it was easier to paint on gold (letters and some details only)..
as to the parts of the icon which contain color you would have to use again peroxide but in much more careful way, because it is easy to distroy an icon.. so you would have to touch the place with cotton bud and peroxide and after to move to another place, and after to come back to the first place, and again to move somewhere else..
So.. try a little if it does the job and how it goes, hopfully it should have varnish so destroing the icon wouldn't be so easy.. if not.. well than you need to be very carefull and patient..
Try this method but on a small peace of the icon, if it doesn't work, although i think it will, than I can call my teacher to ask, but I think her first answer would be the same with mine ( I'm learning iconography in one of the best Byzantine Iconography schools in Greece.. so if not me my teachers will know how to help)
The treatment of the materials used for cleaning an icon - if it is water- the water must, as ozgeorge wrote - go to the sea, river or be left in a church (churches have places for water from after baptism), any other material used to clean like cotton buds, cotton, paper etc. must be burnt. the same thing happens to the paper towells which one uses to clean his fingers after pouring new oil into the oil candle for God. The same procedure. It has to be burnt.
I wish I could help better but my english doesn't allow me to express my thoughts in nicer and correct way... :/