White bricks slightly different, real, fake or old?

[StarrySkies64]

These white bricks are slightly different, one of them has the copyright lego on the bottom and the other only has the ID number and some other numbers on the bottom, and the way light enters the brick is totally different (see photos in links)

They all have the Lego logo on the studs, however.
What is this? Are they old, fake or just a mold variation?

[Mylenium]

This could be a million things, but I'd assume they are completely legit. A few things to consider:

• LEGO have been thinning out walls and supports with new parts revisions
• they have been dialing down the pigment amount and also messing with the base ABS mixture
• they continually experiment and use different pigments
• older bricks may use mineral-based pigments and fillers like chalk that are simply more opaque
• in-machine pigment mixing causes variations, anyway

Mylenium

[Jdrewg]

I should post some of mine, that say "Pat. Pend."

[Peppermint_M]

Yeah, those are all legit looking bricks. As Mylenium said, a lot of older plastic dyes used minerals or metals which makes them opaque. Later laws for toy production meant these got removed in later production runs (later by years and decades) but as all LEGO bricks carry on matching each other, you can pick up 60s and 70s brick that will look enough like modern and that have been kept well there are few signs of their age.