Well, I think the real, but uninteresting answer, is a diamond ring (most married couples have one around, somewhere…), or other jewelry. Very obviously valuable to just about anyone over vast reaches of human history. (The relative value of diamonds over other jewels is higher now, thanks to recent marketing, so other jewels would be a better investment,but diamonds would still be very valuable).
I love questions like these! I’d think a modern printed encyclopedia would be invaluable.
What’s the intent once we land back in the past? Grow rich and change world history?
Nitric acid was well known in the 14th century, but glycerin wasn’t discovered until 1783. That point is yours.
The people recognizing the History of the Hundred Year’s War as valuable book is also a point for you. The OP asks that the item be immediately known to be valuable. Books in the general case fit this best IMEIO.
I’m fairly sure a replacement primer unit could be made that worked by means of a small flint and steel. A jeweller of pretty much any era should be able to make it, further back than the middle ages, certainly.
“Chess is believed to have originated in Eastern India, c. 280 – 550 CE” — Wikipedia
I’m not saying chess was common, but it was around. Any board made from cheap inexpensive wood would not be recognised as having any great value.
The point about an atlas is that right now most households have one. Better would be a detailed map of England, Scotland and France, but most high quality world atlases have pretty reasonable maps of these countries. The value of such maps in the constant bloody wars of the time would be huge. It would not take too long to test the accuracy of the maps in question. Worrying about the existence of other continents could be left to a future generation. But the value of accurate and detailed maps of your competitor nations would be massive. Detailed understanding of the seas would make a serious difference to trade. Would any random merchant grasp this at this time? Probably not. But the nobility and monarchy most assuredly would. So it should not take too long to find someone who would pay richly for such information.
Given the OP drops you into England right in the middle of the plague one might prefer some other simple household items, like rat traps, rat poison and as much insecticide as you could carry. Serious antibiotics are not something that one keeps in the bathroom cupboard, so prevention is about all you would have.
Some random thoughts:
a lighter
Gortex jacket
a good saw and/or axe
A flinter only gets you back to like 1700 or so. One of those would not instantly “have value” in 1400; you would have to prove its worth first. To go really medieval you need to start talking matchlock. And for one of those I would want to hide some electronic ignition system just to be sure.
My thoughts (based upon the OP) tend to flatware (should you be lucky enough to have a set of real silver around the house) or spices. Some good modern knives would be nice as well.
Were I thinking of playing Connecticut Yankee, I would “invent” the flintlock and rifling 2 or 3 centuries early. I could manage either given a little help (physical) using the tech available say 14 or 1500.
To do that, you would also have to ‘invent’ a lot of other things, like some means of accurately boring a tube, never mind cutting the grooves. You would also need a better propellant than the black powder they were using then.
On rereading the OP I see the question is (duh it’s in the title) what will fetch the most cash.
How about a window or sliding-glass door?
I still think that something like a Kindle with a solar charger and preloaded with as much relevant history as I could find. This would enable me to predict events and thus make money.
Window glass would be immediately recognized as having great value. The Connecticut Yankee electrocuted 5,000 knights, does anyone remember how he did that? How did he generate the electricity?
I read a story, possibly in Omni, about a time traveller who went to visit Isaac Newton. The man brought with him a calculator with a tiny nuclear device for power, in the hope that Newton would use it to further his scientific discoveries. It was set to self destruct at some point, possibly after Newton’s death. He demonstrated the calculator by dividing a very large random number by another number. Unfortunately, the answer happened to be 666. Newton, a deeply religious man, determined the time traveller was a demon and chased him away. He threw the calculator into a river, where it exploded some time later.
If anyone remembers this story or, better yet, has a link to the text or at least the issue it appeared in, I’d appreciate it.
Great now that you spoiled the ending for us! Kidding, I’d love read that as well Johnny L.A.
Double post sorry …
Glass and cloth might not be worth “a fortune”, but they were extremely expensive goods back in the middle ages. If you’re like most people you’ve got closets filled with cheap clothing in super-bright colors. Nothing like modern dyes existed in those days, so a cheap t-shirt in a saturated color would be worth a lot just as a raw material. Any newer fibers would be luxury goods, even cotton was an exotic import from the Orient. A great way to make money via a wormhole to medieval times would be to buy up used clothing from thrift stores by the ton and sell it by the square foot. Cloth was literally a cottage industry in those days–any time a woman was sitting down she was expected to be working on one stage or another of some sort of clothmaking.
I still stand by the sewing machine. Let’s pair up and make a bundle. You can name our clothing shop.
Man I didn’t think of clothes, good point. I know purple held a significant place with ancient Romans … What color would’ve been most valuable then and there?
A big-ass nuclear submarine, though I’m not quite sure if that counts as a household item. Otherwise, a powerful telescope or binoculars with cutting-edge optics, or even a microscope, though I don’t know if medieval people would have a use for one.
Telescope or microscope sure but big-ass nuclear submarine? Awesome!