An 1864 advertisement for the masonic jeweller William Platt.
William Platt entered his mark at the London Assay Office on the 10th February 1852 from the address of 12, Sloane Street, Chelsea. The move to 6, Beaufort Buildings, Strand, occured in 1853.
A little more information on William Platt from UK Census.
He was born in Soho London in 1820. According to the 1841 Census he had trained as a diamond setter. He married circa 1840.
After trading at Beaufort Buildings the 1881 Census records him as a masonic jeweller at 4 Mona Villas Twickenham.
Three of his sons trained as jewellers. Another was an artist for a time.
He died around 1882. In the 1891 Census his wife Loiusa is recorded in Fulham as a widow working as an embroideress.
Thanks for that, I'd found very little about William Platt, other than details of his masonic activity. I did find this newspaper report that details a jewel of his manufacture:
"...The WM then proceded to invest Br Parkinson with the jewel, which is formed of 18-carat gold (maker, Br William Platt), and enriched with rubies and a large brilliant."
Source: The Era, 12th April 1863
Besides that, only a bankruptcy notice issued in October 1866 where he was described as a 'Working Jeweller' at Beaufort Buildings.