I got way too curious and decided to sacrifice a Jungle trainer card to test the "light test" and show the internal structure of a non holo card from 1999 - 2000.

Basically, the cards are translucent, not opaque under bright light, but the dark layer should show up as a grainy, splotchy pattern, similar to looking through dark tissue paper. Edge-on, you can discern three main layers under bright light with a steady hand on a zoomed phone camera.

Also, non holo cards are basically five layers: ink-cardstock-black paper-cardstock-ink. Lighter colored cards like colorless energy or trainers are more transparent than blue or green or dark ones.

From the structure, you can understand how surface wear can give you white patches on the front if the wear only removed the top yellow border ink but didn't fully break through the underlying cardstock.

Lastly, after some quick measurements, it appears the correct thickness for a pokemon card of vintage era is about 0.010 inch, or 0.25mm. This is enough for reasonable structural integrity but still only about as thick as two to three typical sheets of office paper. 

Of course, don't forget to look for other obvious fake signs like a water energy fire pokemon, misspelled words, or terrible colors.

Thank you for reading. I hope this helps anyone concerned about buying, selling or apprasing their collection!

Public Service Announcement on Real Cards vs. Fake.