So I remember reading an old Scarne book years ago, and he described a strategy professionals used where the gambler simply intently follows an ace through a shuffle visually and bet the farm when the ace was likely to appear.

I like the transparent simplicity of this idea. The power of an ace is first card is significant. While I doubt there are too many people alive who can predict the exact location of an ace with that much accuracy even adding an ace to a deck wipes out the house edge. If you can narrow a specific ace down to a specific deck segment you can make a lot of money if you can shove down a big bet and spread to multiple hands. The important word being "can".

However I have never heard of an AP in the modern era using this technique. There are somewhat similar techniques such as card steering and sequencing but they are not the same thing.

Scarne was considered an authority on the physicalities of card games especially cheating methods: however he was poor on the mathematics of the game. He was also a massive narcissist and I wouldn't be surprised if he made this up. If he didn't make it up the shuffle procedures during his post-war heyday were very different from now.

I've experimented with this a little and it does seem to work to some extent with a lot of eyeballing practice but you can never really get a statistically significant sample size so it is difficult to know whether you can get an edge. You are looking at one opportunity per shoe. And you don't know if you succeeded most of the time-one ace of spades looks much like another.

Has any one ever tried this? The sheer absence of any information on this subject isn't encouraging but that may be due to the stoically mathematically nature of most blackjack ap's who like their randomness with a degree of certainty.