Update 8/18--Painters: What do you use to replace paint cap gaskets that get old and brittle?

Badger Modelflex acrylic paints, along with their Air Brush line, had neoprene rings for the bottles at one time.  I purchased them with other air brush parts, from the Walthers website.   I found two on my work bench but they don't fit the Scalecoat bottles/lids.  

Probably "all wrong", but i put a piece of aluminum foil over the bottle and screw the cap over it. Seems to work ok.

Get a piece of sheet clear plastic like from windows in toy boxes, or greeting card boxes.  Use a scissors to cut out one circle of plastic that is outside diameter of the bottle and mark the circle rim with a black sharpie so you can easily see and find it.  Mark the pattern with name of type of paint bottle the pattern is for. This is your pattern to make as many more circles of plastic as you need and extras.  Place them an envelope with a paper pocket on the outside to hold your pattern.  Save the pattern so you will not have to remake it.

Do this for Testors size paint jars or other sizes if you have them.  I have been making and using these lid seals for years and have several hundred jars of model paint.  I store them up side down hoping they do not dry out.

Charlie

Get a sheet of thin rubber and cut out your own, using an original as a template.

Cork was used as a gasket also, so you can make them out of cork too.

Larry

Back when I was using the bottles of Floquil I found that the plastic gasket in the lids of some soda bottles would fit the paint bottle caps perfectly.

@mark s posted:

Probably "all wrong", but i put a piece of aluminum foil over the bottle and screw the cap over it. Seems to work ok.

All wrong can be all right. I used to use 2 - 3 layers of Saran Wrap or like material. Seemed to work decently. I did generally  replace it after every use, as it tended to suffer from the cap on-off-on action. 

I use Glad "Press n' Seal".  It has a sticky side that I place on the bottle rim and the smooth side to screw on the cap...makes for a tight seal.

Ace, Home Depot has hundreds of different size O rings. Cheap and easy to use. Don

It really depends on the solvent used in making the paint, but I check the plastic doesn't react for a while.

I've used all of the above, plus cutting it out of the layer of shiny white cardboard between soda cans in a case of pop. The ink seals pretty well, and so does dense cardboard.

(I actually use a large leather cutting punch set most times vs curved scissors or compass blade  )

You can make a hole punch by sharpening a tube or pipe end. Copper, steel, whatever.

THANK YOU for all of the experience-based solutions offered above.

Bought this product at Ace Hardware ($2.99); traced the two different size bottle caps; cut-out with single edge razor blade; and, now have new gaskets for my paint jars (and a lifetime supply of "Fiber Gasket Material" left over):