Mary Denton wears an ornate gown in this portrait by George Gower. The Wikipedia article for George Gower is here.
This is my assessment: The ruff and cuffs of this spectacularly elaborate gown appear to be ornamented with spangles and a great deal of gold and, possibly, silver thread. The material used in the black bodice and over-skirt has a spectacular lining shown in the lapels and by the slashed sleeves.
She appears to be wearing a black over-skirt that merges with a bodice set off by embroidered revers from a maroon stomacher that matches her under-skirt or kirtle that in turn covers a white petticoat or lining. The rounded bodice point previews early 1600s dress and, while the partlet, thick neck, ruff, and French hood are 1500s, the revers and stomacher appear again and again beginning in the late 1600s through to the late 1700s.
KatRowberd has this on elizabethangeek.com/costumereview: "What a beautiful outfit! The colours are bold and strong, and the embellishment is elaborate without being fussy.
Denton wears a red velvet kirtle trimmed with gold and silver bobbin
lace and small white ribbons. It is lined in white, which shows where
she is holding it in her hand.
Over the kirtle she has a black
gown, possibly also velvet, and trimmed with identical silver and gold
bobbin lace. The sleeves are slashed from shoulder to wrist, and caught
along all but one slash with gold filigree buttons.
and showing through the slashed sleeves and in the area of her throat,
you can see she is wearing a very heavily embellished shirt. It's hard
to tell just what form of embellishment is used, however. Possibly very
fine blackwork with gold highlights and spangles, or possibly some
other form of embroidery. Her ruffs (at the neck and cuffs) are trimmed
with bobbin lace and silver and gold spangles.
She wears a
french hood set far back behind her curly hair, and for jewelry she has
a large jewel on the front of the bodice, another hanging from her
girdle chain, another on a necklace inside her shirt, and a gold chain
pinned in three loops across her bodice. She has only a single ring, on
her left hand."