can this spray do any good for cds and dvds?
http://riverproaudio.co.uk/items.asp?Cc=PROTECTIONSPRAY&Bc=
Protect your printed CD’s with specially formulated River CD Protection Spray. Available in 400ml cans with a specially designed nozzle to give equal disc coverage. River’s protection spray finishes inkjet discs to a professional standard with a high gloss waterproof finish. Yeild per can is dependent on how much spray is used per disc.
I read somewhere that these spray can be dangerous, because is easy to spray also the data surface, making the disc more difficult to read.
Even if I never printed a disc, in my opinion these spray are pretty useless however 
People have been using clear acrylic sprays of varying types since printable discs first came out.
Yes, you can easily render a disc unreadable with over-spray.
The watershield / aqua-ace type glossy finishes don’t really need a spray.
But given the cost of printable discs these days, why spend money and time messing with sprays? If it wears out, replace it. If you really want gloss, start with glossy discs.
I would simply buy water resistant media like Verbatim AquaAce.
IMHO, putting any foreign substance onto a cd/dvd is just asking for data loss.
I wonder if it’s not just hairspray, like we used over charcoals in grade school?
I have done more looking into and I do find that buying specific water-resistant media for ink jet spray label I feel to be worth every extra penny. Clients almost always seem impressed by this. No residue, no imperfection from uneven spray or dry.
I never will spray anything onto my disc if i want to store it for long.