Part of becoming a complete trader is becoming a knowledge repository. The more information you have stored in your head, the more accurately you can make decisions in the moment. While I myself prefer not to traffic in foils, because they're expensive and more difficult to move, there are many who do. As such, you need to be aware of certain cards that command a significant premium to their non-foil value. While most foils are worth between 25% and 50% more than their non-foil value, there are some that are worth more than 10 times their base value. These can often be found sitting erroneously in collections or fixed-price boxes, and are real rocket fuel for a trader. From here forward, when I cite a price, assume I mean the foil version unless otherwise specified.

Card: Anything from 7th Edition

Motivation: These were the only core set printed in both foil and with the old card frames. In addition, although 7E was white-bordered, the foils were black-bordered. Some 7E cards had new art which can't be found on any other set. 7E was also opened VERY infrequently.

Pricing: The 7E Birds of Paradise commands a $60 price tag, the Pain Lands are around $10-$15 because of EDH, Arcane Laboratory is in the double digits, City of Brass is $25, Counterspell and Duress are both above $10, as are just about every other playable rare in the set. Most importantly, the lowly Goblin Matron can fetch a $50 bill all day long. You can blame Legacy players pimping out their decks. Infernal Contract, the black card-draw spell, is $25 for the same reasons. Unsurprisingly, Wrath of God is also $50, but you could have guessed that.

Card: Goblin Welder

Motivation: Our dear friends Legacy and Vintage. Welder is a staple in Vintage, where he can recur all manner of horrible monsters.

Pricing: $80, compared to a regular $6. Legacy was the first set to feature foiling, and is sufficiently old enough to make the foils very rare. Most people know about the card and won't put it into foil bulk boxes, but you may get lucky.

Card: Brainstorm, Mercadian Masques

Motivation: The card is a staple in Eternal, as many on this list will be. Masques was the only set to feature foiling and Brainstorm. Eternal players shy away from the FNM promo because the Masques version looks nicer and is harder to find, this making it "more pimp".

Pricing: $30 for the Masques, $10 for the FNM promo.

Card: Counterbalance

Motivation: Coldsnap was not opened much, and considered a failure of a set. Oddly enough, two Coldsnap cards are at the center of two dominant decks in two formats. Failure, my ass. Most sets will only leave a legacy of 2-3 cards in tournament Magic, and Coldsnap has done so.

Pricing: $30

Card: Dark Ritual, Mercadian Masques

Motivation: See Brainstorm

Pricing: $30

Card: Lightning Bolt, Judge Promo

Motivation: These Bolts look just like black-bordered Revised/4th Edition Bolts, but with the old-style foiling process. They're rare, they're gorgeous, and they're "vintage" - not in the sense that they're used in the format, but they're Standard playable with throw-back art.

Pricing: $30

Card: Memory Jar

Motivation: Insane in Vintage, especially with cards like Welder and Metalworker, Jar can enable some truly ridiculous combos. Like the aforementioned cards, Urza's Legacy was not opened nearly as much, or as recently, as many other sets.

Pricing: $40. A non-foil only costs $5

Card: Metalworker

Motivation: See Memory Jar.

Pricing: $35

Card: Misdirection

Motivation: This is like another Force of Will in Legacy and Vintage decks. Often able to outright counter a targeted spell, and sometimes able to hijack an Ancestral Recall, the pitch spell is very, very powerful. It was only printed in Masques, thus foil copies remain rare.

Pricing: $60, $15 for a regular version.

Card: Radiant, Archangel

Motivation: .........? Seriously, why is this expensive? The only reason I can see is for EDH and Casual appeal. Players love angels. Players love Legends. Players love foils. So players must love Legendary Angel Foils. Being from Urza's Legacy, again, is worth a lot when it comes to foils.

Pricing: $50, and don't you ask me why.

Card: Reya Dawnbringer, Invasion

Motivation: See above.

Pricing: $50, and at least she's insane in EDH.

Card: Rofellos, Llanowar Emissary

Motivation: EDH, EDH, EDH. The guy makes a sick general. Since EDH players usually keep their cards for a long time like Eternal players, they tend to want to foil out their decks, and the General is no exception.

Pricing: $50

Card: Sensei's Divining Top

Motivation: Just like its cohort Counterbalance, Top is essential to Legacy Counter-Top decks. It would only stand to reason that Top foils appeal to Legacy players.

Pricing: $30 for CHK, $15 for FTVE, $7 for regular

Card: Swords to Plowshares, Old-Style FNM Promo

Motivation: It's freakin' StP! You kids these days and your Path to Exile. In my day, we could remove creatures from the game and no one got a free land. Now, you have to give a guy an extra land in order to whack one of his goons.

Pricing: $35, for the old-bordered, old style foil Promo. Looks just like a Revised Plow but foil.

Card: Unmask

Motivation: Similar to Misdirection but less essential to the format, Unmask is a crucial "free" spell in Eternal formats.

Pricing: $35

Card: Wasteland, old-style Player Rewards Promo

Motivation: The card is already a format staple in Legacy, and this is the only way to get one in foil. What, you thought it'd be cheap?

Pricing: Actually, it's not that bad at $40. Wouldn't shock me to see this one go up.

There are certainly other expensive foils in Magic, but these are some of the really remarkable ones. It's clear that the real driving force behind Foil prices are the Eternal formats, including EDH. Many players don't like to foil out Standard decks since the cards rotate so quickly and decks fall in and out of favor almost weekly. In Legacy, however, decks can stay viable for years, and many of the same staple cards are shared between decks.

If you're digging through a box of foils, pull out anything that catches your eye. It may not be rocket fuel like the cards on this list, but if they're inexpensive, it's often worth a gamble. I personally don't recommend trading in foils, but there are many, like Jon Medina of MTG Metagame, who are just brilliant at it. If you have the knowledge and time to learn what trades well, and you have a regular outlet for these foils, then by all means, jump right in. They're not good for newer traders, as the chance to get ripped off or stuck sitting on an expensive card for a while both exist.

With any hope, we'll have some Rise of the Eldrazi spoilers to discuss soon. I'm not holding my breath but it would be nice to see some more by the end of the month ;)