Plaques with hand-painted birth dates, deaths and other anniversaries are very attractive to collectors.  The three plaques above, from Sunderland Museum & Winter Gardens, Tyne & Wear Archives & Museums, help us to date this particular form as circa 1860.  A word of caution though, birthdates might pre-date a plaque and sometimes by many years, eg if the plaque was presented as a 50th birthday present.  Dates of death are perhaps more helpful in terms of dating, although the third plaque was likely commissioned 20 years after William Burn died. 

The two plaques above now reside on different continents.  Perhaps there is a third 'Quick' sibling's name somewhere on a 'Thou God...' plaque.  It seems likely that these were both commissioned in 1875 (the date of birth of the younger child).  Thanks to Dr S Nield for providing the following information:

On your site, you have pictures of a pair of plaques which have birthdates and names specially inscribed on them: Mary Lizzie Quick and William Daniel Quick, and you mention that there might be a third [plaque with another sibling] out there somewhere. Actually, there could be two more: one for their sister Henrietta (born 1882/3) and one for their brother George (born 1879/80). I looked them up in the census records: they were the children of Cornish fisherman William D. Quick and his wife Mary Noall, both born in 1840 or so, and they all lived in St Ives. (Mary Lizzie from the plaque married a man called John Thomas in 1888).

Interestingly, there is no Sunderland link.  So perhaps these inscriptions were added by a local distributor, rather than commissioned from a Sunderland pottery.

Two superb hand-painted plaques with gilt and black borders.  Inner border of acorns and leaves.  Dated 1840.