I just use silly putty.  You probably will need several "eggs" for a good sized model and can fill in the gaps with tape or post it.

Once when I used it I left it on a long time and it did some discoloration so take it off as soon as you can.  Also, be careful of the strings.

I just built a 1/72 scale Tiger with my 7 year old and the camo turned out great:

--Panted tank green and outlined camo pattern with rolls of sill putty.

--Painted panzer brown.  Then squished sill putty.

--Painted dark yellow.

The result even in 1/72 scale was a cool pattern of green camo with brown edges.  We airbrushed for a soft edge finish but you can push the edges down and get a hard edge finish.

I made use of silly putty for this cammo job and was happy with how it worked

One nice job on the Phantom.  She is loud and proud.   It appears the silly putty worked well for you.  My spitfire is not at your level, but being my first masking job its ok and I learned a lot.  I liked using the silly putty.    Bud      

I personally use PlayDoh - easy to find, dirt cheap and it does a great job for sharp edge camo.

I think SP works great! I used it for the first time on this Phantom:

I had always either cut out little paper masks for camo or attempted free hand patterns. This was easy once i got the hang of it. My secret was to roll a small piece into a long rod, lay it out into the pattern I wanted, press into place and the fill it around the outsides with pieces flattened by hand. It sticks instantly to itself! (Caution there!) Lightly press into place and begin painting! I haven't had any problems with the old paint-just knead it into the putty and it still works!

I would check with toy stores, also my local Hobby Lobby stocks it- I also spotted it at Walmart and Kmart. You can also order it from crayola if it is too hard to find:

Silly Putty!

Wikipedia says this:

"Scale model building hobbyists use the putty as a masking medium when spray painting model assemblies" under 'Other uses'

Complete article is here:

Wikipedia

Just my view here!

I've been using the putty for the last two days and so far it has mixed rather well.  Noted that if you have hard chips in the putty they can play some havoc with edges.  I do believe the putty does have a shelf life, but for how long I have no Idea.   I have a P-51 sitting in the wings so i think I'll try the tac type putty with it.   Bud

I've gone ahead and camo my  Spitfire.  For first time and still learning the AB's.  It doesn't look to bad, but I've a lot of touch ups and light sanding.   Call me goofy or nuts, but there was areas that looked and worked liked the paint and silly putty was attacked to each other, or at times they were opposing each other.  Can static electricity play a roll in all this?  I'm using Testors acrylics on the Spitfire  with several light coats.  It just didn't seem kosher know what I mean.   Bud     

BBAT222

Well thanks to you guys I'm finding out there's several putty types to play with.   Silly Putty must be kind of new to  the scene.  I take that all these putties must be impervious to all types of paint.  They do call silly putty a solid liquid.  Thus it must still flatten out even after it been painted.  

I take that the other putties must keep their form once put in position and heat and cold probably don't bother them.  When using these putties do you change the thinner paint ratio from the normal ratios.       

Not too sure if Silly Putty is all that new - i've seen some older articles where they talk about using it.

However, i think it might just be harder to find than blu-tac, u-tac and all those other types of 'putties'. 

As for thinning ratios - keep them all the same as if you're painting a normal model.  The putties are merely masks and the paint shouldn't affect them.

I've used both the yellow tack and Silly Putty. Both work well but I think the Putty works a little better. I did a three colour scheme with it and left it on for a couple of days without problems. I was a little worried at first since it has a slightly greasy oily feel to it and might leave residue on the model but when I peeled it off it didn't leave anything.

Well thanks to you guys I'm finding out there's several putty types to play with.   Silly Putty must be kind of new to  the scene.  I take that all these putties must be impervious to all types of paint.  They do call silly putty a solid liquid.  Thus it must still flatten out even after it been painted.  

I take that the other putties must keep their form once put in position and heat and cold probably don't bother them.  When using these putties do you change the thinner paint ratio from the normal ratios.       

Hello!

In my parts we have stuff that must be similar to the bluetac, it's called Patafix. There's also a very similar product by Faber-Castell. I also had no problems reusing it, and left it on my model for several days. When it happens to leave a slight residue on the model, just take a piece of clean Patafix, stick it to the place with the residue and lift off again - it usually comes off taking the residue away. I usually roll a kind of "cord" out of it, which I use to outline the colour boundaries. This way I can get colour transitions that are not 100% sharp (as with masking tape), but just very slightly feathered. That's realistic for many aircraft, where the colour transition only has about an inch in 1:1. So the thicker you form this cord, the more feathered the colour transition is on the model. Hope it helps, have a nice day

Pawel

There is also a yellow colored poster tack out there which I've used.  It works best if you knead the stuff in your hand to warm it up.  It makes it more pliant.

You can remove it by rolling and pulling it off.  It will come off in clumps.  Smaller pieces can be picked up by pressing a larger glob on the piece.  It will usually come up with very little problem.

As the others have said, it can be re-used.

I only leave it on long enough for the paint to dry.  In come cases I've taken it off in about an hour, but maybe wait a day.

Good luck.

Reusing isnt a problem, wait for the paint to dry then work it like you would before using it to stick something on. breaks the paint up into tiny fragments. Ive got white tac which has now gone grey after using green, brown, grey and white on it. Still just as maliable, just every so slightly grainy.

I can't comment on silly putty (in fact i can't find the stuff in Australia - if anybody knows where to get it here, please let me know).

On blutac - i reuse it over and over and it still works pretty well.  One thing to note with it though, as Scorpionmikey said, it's pretty sticky and should be removed asap.  I've made the mistake of leaving it on in wheel wells for the duration of a build (which was about 2 months) and it became extremely difficult to remove from around the details.  Required a toothpick to pick out, which then lead to me removing paint which required touch up etc etc.

Chris.

I've been curious about whether or not you can keep using the silly putty once it's been painted.

What about the blu-tac?

I use a stuff called blutac. Works freakin wonders, i love it. Its similar to silly putty, but stickier, usually used to put stuff on walls. doesnt leave any residue either. Only issue i have with it is its kinda hard to get into shape, i imagine silly putty would be better.

The other issue i had (just remembered) when i did a vertical surface some of the paint welled in the join between the tac and the model. ended up with a scummy line.