18th Century Bonnet Images
Since only one 18th century bonnet exists (that I know if. If you know more, please tell me!), almost all of our bonnet knowledge has to come from paintings, engravings, and other visual images. Here are some of the images I've collected that show bonnets.
The only known extant bonnet, in the collections of Colonial Williamsburg. Dates from 1770-1780.
A Lady Standing, by Daniel Chodoweicki. 1759. This is the oldest bonnet image I have come across. You see descriptions to black silk bonnets beginning in the 1730s and 1740s, but almost every image is from the 1770s on. This is an exciting image!
This is another Chodoweicki from 1759, and there appear to be several bonnets in this image. I've highlighted the ones that I think may apply (though the one on the top right could be a guy...).
Francis Wheatley, 'A Market Scene', 1770s. This bonnet is interesting because you can see that the brim is lined with a lighter color silk.
An engraving from the novel 'Cecelia' by Chodoweicki, 1787. Look how enormous the brim of her bonnet is!
Also from 'Cecelia'