There are a ton of tutorials, but I can certainly add another haha
I like to use these sponges..
the makeup wedges. The cheap ones which you can pick up in dollar shops and department stores or supermarkets. I've seen others use various sponges, but these are the ones that work for me.
Lately I've been using a few different colours to help brighten these horrible winter days :)
Start by applying your base coat. In a lot of cases that may be white, or the lightest colour you plan to sponge with. I prefer to use my lightest colour - however yellow pops better over a white base, as do some other lighter polishes. If you're going for Galaxy nails, it may be a black or a dark coloured base.
There's really no limit to how many colours you can sponge at any one time, providing you have the nail space! Gradients are typically a couple different colours sponged so that they mesh/blend together. Sometimes they're from the same colour family, sometimes a progression from light to dark - the possibilities are endless.
Colour by TBN Yellow, Profusion Mint & Lilac, Sally Hansen Fruitti Petutie, Sinful Colours Snow Me White (base)
The sponges can be reused several times. I simply cut off the end with the last lot of dried polish. Any part of the sponge can be used, so they can be any shape. I have found thinner round makeup sponges too thin, the polish seeps through and gets all over your fingers. I do like the thicker end as its a pretty good size. Sometimes I use the smaller end to apply a single colour.
One of the biggest tips I have to share with you is to lightly (very lightly) dampen the sponge. Very lightly. (Just the end you're using) This helps to keep the sponge from soaking up too much of the polish before you can get it on! I simply add (in this case) drops of the polishes in the positions I want them. It's usually a good idea to add a second drop before sponging on your nails as most of the first has already seeped in. But not so thick that it will drip!
In the photo before this one ^^ you can see that the green I chose to apply wasn't opaque enough for sponging, so I switched it up the second time around with Duri Pie in the Sky Green.
After approximately 3-4 coats I was happy with my colours and coverage. I did apply some extra yellow on its own, simply held the sponge on an angle to ensure only the yellow area touched my nails.
Cleanup can be a real pain after sponging. Especially if you use a red which stains like nothing else! Or black! It's all trial and error! I know some people like to apply a PVA or Peel Off coat around the nails (on the skin) to aid cleanup, but I don't find it any easier.
I prefer to use cotton buds and acetone for the bulk of the cleanup around my nails, but go in with a brush (mine's an e.l.f concealer brush) for close cuticle cleanup.
I do really like the bright multi coloured manis in winter. Yellow is the most eye-popping colour against the dull grey skies.
Here's a white to peach gradient - the first time I've done one like this.
I've used Sinful Colors Snow Me White and Ulta3 Peach Paradise. Again I did a white base, only a thick single coat. I then used both the white and the peach vertically. Rather than add drops of polish to the sponge, I apply it thickly across the sponge. I repeated the sponging a couple of times, including using only the peach to apply it a little darker on the ends.
I also figured why not add some stamping. Using plate CH10, I actually used the same two polishes to make the stamping in the reverse colours. (First time I've done multicoloured stamping)
I think I need a little more practice placing my two-tone stamping, the pinkie turned out perfect!! But yes.. I had to add the peach on the thumb and stupidly turned my stamper and it came out crooked!! Ooopsies!! Not real noticeable IRL :P
So there you have it. I hope you can make sense of it all. Like most things, its all trial and error. Work out which polishes are opaque enough and which ones stain your skin like nothing else :) I'd love to see any sponged manis you create. Galaxy nails are by far my favourite sponged look, you do have to work out which colours will sponge over black before hand, alternately lightly sponge white in the areas you want the colour then add them :) Good luck! And have fun xox