Unsurprisingly, many artists known as ‘Walker’ were active in the 18th century, and it is difficult and perhaps incorrect to differentiate between their works. J Walker may have been the miniaturist Walker, active in the 1770s and recorded without initials or the painter James Walker, also active in a similar period. There is simply not enough evidence to positively tell. The J Walker known from one silhouette painted in Trowbridge, Wiltshire worked simply on card with blackened and white paint. The sitter’s dress suggests a mid-to late 18th century date.
Source: McKechnie (Author of, British Silhouette Artists and their Work 1760-1860)
Walker, J. (McKechnie Section 2)