The top half of the stone is covered with a continuous abstract La Tène style design similar to that on the Castlestrange stone in County Roscommon. Concentric spirals are carved in low relief to the depth of about 3 cm.
It was for centuries a curiosity at a lios, or fairy fort, some 3 km from Bullaun, but was moved to the present location at Turoe Farm, in the late XIX Century. It was probably saved from vandalism or worse, but the historic provenance has been destroyed. Some historians have claimed that the stone was carved in France, brought to Ireland in Celtic times and ultimately, like some family heirloom, moved further west, far from the prying eyes of the invaders. The religious or ceremonial purposes of the stone are lost in time.
George Coffey, in his 1904 paper for the Royal Irish Academy on the subject of La Tène art, said that the stone had been moved in the 1850s from the rath of Feerwore site.
The Desborough Mirror has a reflecting surface with green patination; the back of the mirror is highly decorated. The mirror is made from three pieces — a cast handle, the main mirror plate and a tubular binding strip around the edge. The pattern is very complex. It has a symetrical outline in the form of a lyre with flanking coils. The pattern may have been laid out using a pair of compasses. Parts of the decoration are engraved, using a graver, with a basket-weave pattern and hatched texturing to make the pattern stand out.