Well known by artisan glaziers and stained glass professionals, this traditional glazing putty recipe is very easy to make:
simply mix 4 parts of chalk powder* with 1 part linseed oil. The consistency of this blend will be like sticky chewing gum.
Add more chalk powder as needed, to obtain a less sticky, slightly thick paste.
Scrape away old putty, then (before repainting, as shown in the example) apply the new putty using a putty knife. Smooth with your finger.
This putty will be fair-colored, similar to the natural color of linseed oil. To make white putty, use refined linseed oil.
You can also color your putty the full range of grey all the way to black using lampblack, a natural dye.
Before repainting, let the putty dry anywhere from one to three weeks. Driers can be added to speed up drying, but are often toxic.
* Chalk Powder: Finely ground natural chalk. It can be found in the cement section of home improvement or pool supply retailers in 3 or 10 lb packages.
Also used to clean marble or silver. Price: approx. $1/lb.