Forum Flora Germanica

I assume left is fresh, right most = middle brought into house after 12 hours.
http://agrozoo.net/jsp/Galery_one_image ... adeaf7d691 ?

So looking at upper for a while and this: http://agrozoo.net/jsp/Galery_one_image ... fd7f9cbb0b
the color of 'inner' and 'outer', at presumably ripe state, is inverted ....

Hi,
I don't know if this is Diderma cinereum. There are several very similar Diderma species, as well as species from other genera that can look similar. As always, it depends on microscopic details: Spores, whether a columella is present or not (present in Diderma) - if so, what it looks like, details of the capillitium.
Even if we assume that it is Diderma cinereum, there are hardly any pictures where the development is documented. For that you have to take something home (as you did) and hope that it matures normally and typically. This is often a problem, slime moulds are tricky. (I once did this successfully with a Stemonitis species and photographed it).
Occasionally you see pictures of different stages: semi-mature to mature to decay, usually it says "Plasmodium unknown".
I don't know what it looks like when the harder peridium (in Diderma consisting of lime granules) forms, where and how this starts.
I saw a picture from New Zealand (if correctly assigned?), which is very similar to your picture. It seems as if the whitish material (lime) forms first on top of the unripe globules.
See the last picture here:
https://www.fungi.co.nz/slime/family/di ... idym10.htm