In 2008 I acquired a very mediocre looking yellow Sapphire. Had a huge window, and I knew I couldn't sell it 'as-is'. So I went to work on it over two days. Started out at 53cts and finished up over 31cts. It may have improved in brightness, but gave up some of its color. And this is why recuts of windowed stones don't always work out.
Before:
Roger is correct especially when there is a huge loss in carat weight such as his example where almost 40% of the total carat weight is lost. When a stone becomes smaller, the light path also decreases, therefore tone and saturation will take a dip. How significant a dip depends on various factors. The best candidates for recutting are generally overly deep stones that are clean. A shallow stone is usually best left as is.
and the loss can be more than 40%.....who can afford that kind of loss when the stone is under 10 carats?! all the above as to why i am no fan of buying to do a recut.