The filler is largely inert and does not change composition when mixed with oil. The reaction is reversible, so if you add water to plaster, and allow it to dry, it turns into solid Gypsum. If you heat up Gypsum, it loses 1.5 molecules of water and turns into Plaster of paris, Calcium Sulfate Hemihydrate. Gypsum is Calcium Sulfate Dihydrate, CaSO4.2H2O. a mixture of calcium carbonate CaCO3 and calcium oxide CaO If Calcium Carbonate only is it simply the oxidation of the oil that makes it go so hard over time? Chalk is chalk. what most people call "chalk" as in blackboard chalk is actually gypsum. Does such a beast exist in Australia? Ironically, the bedding putty on the inside of the glass still has a lovely red-brown colour. I can't find brown putty though (except in the UK). What I would prefer is to use brown-coloured putty similar to the frames so that I could paint both the frames and the putty with Sikkens.
As we use Sikkens on the cedar, that would mean I'd have to be very careful to paint just the putty and not splash it onto the timber frames. The glazier has also suggested I could paint the putty so it blends in with the cedar frames. That didn't sound like a long-term solution so I have laboriously scraped out all the outer putty bead (with the help of a Dremel). He's suggested that trying to remove all the putty risks cracking more panes.
The glazier has suggested that he could remove the broken portions by "flicking the loose bits out with his finger", then filling in the gaps with fresh putty.
The windows that are not cracked though have partly-broken putty. A glazier will be replacing several cracked panes and they obviously will have fresh putty. I have ten 40-year-old casement-style red cedar windows where the putty needs to be replaced.
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