Leonardo created the sketch of the Marchioness Isabella d’Este in 1500.  It reveals pinholes punched into the sketch for the purpose of pouncing.  A method commonly used to transfer a drawing before painting it.  

Holes were punctured along the lines of the drawing of Isabella.  Laid over the poplar panel, it would have been dusted with charcoal.  The dust passing through the series of holes along the outline, would have formed corresponding dots on the surface below.  The artist could use this as a guide for the composition of the painting. 

The apparent pinholes reveals Leonardo used pouncing to transfer Isabella’s image for a painting.  The sketch of Isabella is punctured along the lines with tiny pricks.  Leonardo transferred this image into panel.  The holes reveal Leonardo intended to transform the sketch into a painting.

 

The sketch Leonardo made of Isabella, correlates with the dimensions of the painting, La Joconde.  While the perimeter of the painting is larger than the sketch.  The images found within the sketch are identical, to the size of the images found in the painting.  Leonardo uses the image of the subject and frames it with a larger, elaborate backdrop for her finished portrait.

 

Leonardo did not use a standard size to create portraits.  Isabella’s sketch matches only the painting, La Joconde.  The other portraits, finished by Leonardo are smaller.  The first, Genevra de Benci is 14.9 by 14.6 inches.  The second, Lady with Ermine of Cecilia Gallerani is 15.4 by 21.3 inches.  In comparison, La Joconde is 20.9 by 30.3 inches.  Larger than the combined area of Leonardo’s other portraits.

 

Visible pinholes reveal, Isabella’s sketch was used to create a painting.  The subject seen in the sketch mirrors the painting.  The size of the sketch and painting subjects are identical.  Validating, Leonardo used the sketch of Isabella d'Este to later create the painting, La Joconde.