This painting of Elizabeth Roydon was completed in 1563 when she was aged 40. The artwork was painted by the Dutch-born Jan Eeuwowts, better known in English as Hans Eworth, and there are over 40 paintings by him that have survived. It’s not known for sure, but it may have been that Eworth was the court painter during the period of Queen Mary I’s reign between 1554 and 1558. Roydon was wearing all black as her second husband, Cuthbert Vaughan (1519-1563), had just died in a military engagement in Le Havre in France. She was though later to remarry a final time, to Sir Thomas Golding in 1564.
This is beyond my art knowledge (as most things are), but the gallery notes that “the present painting is in extremely good condition for its age and, with its very fine brushstrokes, is carried out in a technique similar to that of a miniaturist. The translucency of the paint in the flesh areas means that the freely drawn underdrawing is now visible”.
The heraldic arms in the corner of the painting were also added later on, for reasons likely related to wanting to prove some heritage line. The Tate acquired the artwork in 1972, when it was bequeathed to them by Miss Rachel Alexander and Miss Jean Alexander.