Plaques with irregular crackle

In April 2010, I wrote about a group of plaques with distinctively moulded borders, without shells.  Please click here to read again, before reading this post. I recently bought the two plaques below, which from the front look almost mint.  But they both have an unusual pattern of crackle on the reverse. N.B. I've greatly turned up the contrast in Photoshop to better illustrate what I mean.

Thanks to Ian Holmes for providing the following photos, which confirm that extensive irregular crackle and stress marks are a common feature of plaques from this unidentified pottery.  Again, I've turned up the contrast on Photoshop.  Click on the images to enlarge.

On some, the crackle continues on the front (see below left). On others, the stress marks penetrate right the way through to the front. This is particularly noticeable around the hanging holes (below centre).

The plaques above tend to sell for high prices, so it would come as some reassurance if we could lay to rest the idea they may be 20th century reproductions.  Have a look at the Adams plaque below.  Again, I've turned up the contrast to better show any crackle. In fact, the reproduction plaque shows none of the signs of stress of the plaques above. The surface has a very, very fine and even crackle (if that isn't overstating it), of a kind I feel I've seen before on 1920's or 30's pottery. So nothing like the plaques above.

Unfortunately, that doesn't bring us any closer to knowing which pottery made the other plaques.