Nameboard fretwork apertures backed by coloured silk were generally used by makers from about 1800. There were various designs and sizes but there were normally two fretwork panels positioned in symmetry towards each end of the nameboard and one internal fretwork in the left-hand back corner of the instrument. This feature in square pianos was patented by William Southwell, a maker from Dublin in 1794. (Patent for improvements in the pianoforte, No.2017, 18th October 1794) and the earliest known extant example of a square piano with fretwork is at Croft Castle, a National Trust property near Leominster, Herefordshire. The nameboard is dated 1784 but this assumed incorrect and a later addition. It was likely to have been made about 1793, the year before the patent was granted.
A Southwell square piano at Croft Castle, Leominster, Herefordshire, England that shows the nameboard fretwork. This is probably the earliest example of this feature.
While it is possible to find various colours of original silk used to back the fretwork apertures on square pianos the majority of instruments used a slightly blue, sage green coloured silk that was probably obtained by piano makers from Spitalfields, the centre of silk weaving in London. Later 19th century square pianos often used red silk.