As we reported, Bonhams' sale of Fine Books and Manuscripts last weekend included some early watercolours by Beatrix Potter.

Before the auction we noted that the affection felt for Potter's works is sometimes underestimated. Back in November 2009 we reported on a selection of original works by the writer, artist and scientist which easily beat their estimates at Bloomsbury Auctions.

The illustrations on offer at Bonhams are associated with The Amiable Guinea-pig and will make an excellent investment.

To be precise, this sequence of 5 vignettes was drawn in 1893 and three of them redone years later for The Amiable Guinea-pig from Appley Dapply's Nursery Rhymes, first published in 1917. Potter's journal entry for February 5th, 1893 recounts:

"I went to the Pagets somewhat guilty. This comes of borrowing other people's pets. Miss Paget has an infinite number of guinea-pigs. First I borrowed and drew Mr. Chopps. I returned him safely. Then in an evil hour I borrowed a very particular guinea pig with a long white ruff, known as Queen Elizabeth.

You can buy a lot of guinea pig clothes for $85,400...

"This PIG - offspring of Titwillow the Second, descendent of the Sultan of Zanzibar, and distantly related to a still more illustrious animal named the Light of Asia - this wretched pig took to eating blotting paper, pasteboard, string and other curious substances and expired in the night... I suspected something was wrong and intended to take it back,

"My feelings may be imagined when I found it extended a damp - very damp disagreeable body. Miss Paget proved peaceable, I gave her the drawing."

The Amiable Guinea-pig is among the earliest of rhymes that Potter used for the 1917 work, and the illustrations were listed at $12,000-18,000. As we expected, however, bidders pushed things a little higher...

To be precise, the illustrations left the stage for an extraordinary $85,400.

Collectors interested in investing in the illustrations of children's authors may wish to take a look at this unique piece related to an entirely different Potter:  a wonderfully illustrated horoscope lovingly prepared by J K Rowling for a child.