And if you can't be bothered, choose Minwax Satin Poly (aerosol) and be done with it.

Tiehwen and the theologian are right on the money!

This is the most useful (and "true") reply for now by far, so do it if you want to apply properly the polyurethane varnish.

Keep in mind that by applying it with a cloth you will prevent the acumulation of any excess of varnish that might happen if you applied it with a brush.

It's even also useful if, between coats (best not more than 2 or 3), you could just sand slightly with sandpaper. I will take the plunge and say with a 240-340 grit but I'm just no sure of that so if any pro around here could just validate my words, please.

If you do this, I think you would do just fine and I'm pretty sure you will obtain outstanding results.

But, if you really want to get what I think are the best results (at least for me), I would you recommend to utterly skip this sealing method because polyurethane tends to change the touch of the blade even if you carry out it with the variation mentioned above: it tends to become more rigid, loses some of the "good vibrations" if you are using an all wood blade,...

Here it comes what I think it's the best method of sealing the blade (at least for me). What I recommend you to do is to use a family of products called Hardwax oils. There are many brands out there that sure will do the job flawlessly but which I've just tested so far with unbelievable results is called Polyx-Oil, by OSMO. 

Keep in mind that this product is made of natural oils and waxes and it needs to penetrate the wood. The advantage I find more useful about it is that it maintains the original touch of the blade (some might think it even enhances the natural feeling of the wood in the composition of the blade, but it's a wild guess).

You need to apply directly to the wood so, if you have sealed the blade previously with polyurethane or with a water based varnish you should sand it thoroughly. 

Then lightly (=not too much becouse the blade simply does accept the amount it can till it saturates itself) apply it with any kind of Scotch Britte scourer (=don't know why but by doing that the oil penetrates better to the wood), if not possible then apply it with an old rag. 

The next step is to allways after 10 minutes or less (here I'm not so sure becouse I think there are others who wait more and others who don't) remove any excess of oil on the wood. Use an old rag for better results.

Then optionally you can sand it with 240-340 grit sand paper but it's not really compulsary, just do it if you want smoother finishes.

if you don't have any specific sealing stuff it is also possible to use hair fix spray. 

something like this

I really appreciate your help!!!

Thanks to you, I can proudly say: "I've seen the light"/ "I've seen the right path"/... and stuff like that.

P.S.: for those who don't know, Magic_M was "the one" who gave me the wise advice to use Hardwax Oil.

P.P.S.: thanks again. You are the man.

Zissner Sanding Sealer, reasonable protection, slight change in the hardness of the blade.
Minwax, great protection, won't ever splinter, but you are basically putting a very thin layer of plastic on top of your wood.

jfolsen

It's water based, so non toxic, and with two layers it adds 1g or less to the weight of your blade.

I buy it in my country for 6 euros for 100 ml from Joola representative, but i can see that it costs 11.95$ on megaspin. I used it on all my blades without any issues what so ever. It protects the blade as good as any other sealant, and it doesn't have that high gloss finish when it dries, but more of a soft satin look.

Here is my Infinity treated with two layers of Joola varnish:

Here is varnish more notable. A close up side view with sunlight bouncing of the surface of the blade

When you unscrew the lid you have a brush mounted on it, but it's of a bad quality, so i use sponges to apply it, the same you use to apply glue.

Another big thing to notice is: i often tryout blades with rubbers glued on before i seal them, than i take off the rubbers gently, seal the blade and glue them on again. I didn't notice any change in performance in any of the blades that i used Joola varnish on. Up until now, i sealed Clipper Wood, Stradivarius, OSP Musko, OSP Virtuoso, JOOLA Greenline Extreme, Joola K7, Killerspin Diamond CQ and few others, and i beleve that they all kept their performance and sound the same before and after sealing with this varnish. Maybe a player with more sensitive touch and hearing can feel the difference, but i just couldn't.

You have instructions on on how to apply it on megaspin or joola's official site. Just google it, and you wont miss it.

Hope i helped a bit.

EDIT: I updated the price and added photos.

I use hair spray (two coats), and I find it did not work on some of my blades. I think it depends on the finish of the blade's surface. 

nail polish remover