Baker's Pure Rye 1847
PROVENANCE | LABEL | GLASS | SEAL | RADIOCARBON DATING
When authenticating rare wine and spirits, it's key to analyze the glass bottle itself. Fakers tend to use glass that mismatches the era when the whiskey was supposedly sold.
For instance, in Unforgiven, when Will Munny (Clint Eastwood) tips a whiskey bottle to his lips, the audience thinks, "Uh-oh. Will swore off alcohol years ago, and now he's drinking!" But you know what glass experts think? "Uh-oh. That's not an 1881 whiskey, because bottles like that weren't manufactured until 1934!" 
Okay, it's a stupid criticism. But to a trained eye, it looks as out of place as a lightsaber fight at the O.K. Corral.
Bill Lindsey is the expert behind the Bureau of Land Management's Historic Glass Bottle site. He took a close look at the Baker's bottle, and concluded:
"It is an American made bottle dating from about 1850 to the early 1860s. The main key to the aging of the bottle is the iron or bare iron pontil mark on the base."
Bare iron pontil scars come from the way the glass bottle was held during the finishing process. They leave a distinctive "smear" in the bottle's base.
Remember, Bill is looking only at the glass to determine any time this may have been manufactured, regardless of what the label says or anything else.
The tool that left the marks was very specific:
"It was rarely used after the early 1860s and was totally obsolete by the end of the Civil War . The bottle likely is no older than the early 1850s, but that is harder to pin down since similar items were made in the 1840s to some extent."" 
Bill put the odds at over 99% this is from the late 1840s to early 1860s. We'll continue to talk about the glass in...
The Seal >>
 For the rare reader with a passion for Unforgiven plus glass bottle dating, the base of the bottle shows the signature pattern of post-prohibition glass codes.
 Just to be doubly sure, Bill was asked how certain he was of this dating. He explained, "Based on my experience dealing with hundreds of such marked bottles over many decades, I would estimate the odds at well less than 1% that the subject bottle postdates 1865." The remainder of that probability is that the bottle dates from "a bit later, since the same workers and tools were still around the glass factories for many years after the general end of use of that method." That still wouldn't challenge authenticity, only Bill's virtual certainty that it doesn't postdate the Civil War. He goes on to say, "It is extremely unlikely that bottles were produced using that type empontiling tool after about 1865," and puts "the odds that it is from the late 1840s to early 1860s at 99+%."
 Some readers familiar with glass dating may wonder why I don't discuss things like bottle seams or air bubbles. The focus here is on the key aspect that winnows down the dating of the bottle, whereas things like bubbles and seams cover broader eras.