Last week, to prepare for the much-anticipated game between Bayern and Dortmund, I dusted off my album of old football autograph cards, looking for Helmut Nerlinger, the father of Bayern Munich's current general manager, Christian Nerlinger.
In the 1970s, Helmut made 122 league appearances for Borussia Dortmund and was a key player in the side that won promotion back to the Bundesliga in 1976. His stint in the Ruhr area explains why his son, who would later play for both Bayern and Borussia, was born in Dortmund. That's so many cross-references that I guess you can see why I went rummaging for Helmut Nerlinger's card to get in the mood for Saturday's match.
The card I have is from the 1976-77 season, Dortmund's first back in the top flight. Nerlinger strikes one of the classic players'-card poses: squatting, eyes fixed on the camera, hands resting on a football.
It's an adidas ball. The imprint reads "official World Cup 1974" and, since it is an all-white model, it must be the ball that was rather bizarrely known as adidas Chile.
(Most people associate the adidas Telstar, more precisely Telstar Durlast, with the 1974 World Cup, the ball that had the black-and-white panels. However, there were actually two match balls used during this tournament. The second one was all-white and called Chile Durlast to commemorate a similar-looking ball that had been kicked about at the 1962 World Cup in, well, Chile.)
I registered this detail somewhat subconsciously and was about to shelve the album again, when suddenly my gaze fell upon Herbert Meyer's card. You mustn't feel embarrassed if you haven't heard of this man. He isn't well-known, though he played a dozen years for four clubs in two divisions.
Meyer strikes a different but no less classic pose: he is standing, his left hand on his hip, his right foot placed on a ball. And it's this ball that caught my eye.
It's not the Chile model. It's not even an adidas ball. In fact, this proverbial pig's bladder isn't German at all. It's a ball you never see these days and rarely saw back then - a Surridge Cobbler. Coming across a Bundesliga player with such an unusual ball aroused my curiosity, so I conducted a brief investigation.
It turned out that Surridge is an English company, formed as early as 1867 by the grandfather of Stuart Surridge, a famous cricketer. Obviously, the company began by producing cricket balls and bats, but eventually it branched out into football and, according to the company website, "developed the Surridge Cobbler football, which was the first lace-less football to be developed and the first of the modern footballs".
Intriguingly, the website goes on to say that "the Surridge Cobbler was chosen for the 1958 World Cup in Sweden" and explains: "The ball was taken to Sweden by the England manager of the time, Walter Winterbottom. The British ball was tested and proved to be better than its competitor balls after it was catapulted 20ft further than its closest rival."
In all likelihood, this is plain wrong, because the official World Cup ball in 1958 was the Top Star, produced by a Swedish company called Sydsvenska Laderoch Remfabriken, based in a town north of Helsingborg by the name of Angelholm.
However, the interesting thing about Surridge's claim is the small detail about the 20 feet, because the 1958 balls were indeed put to such practical tests on a pitch by a group of functionaries that included Sir Stanley Rous. The World Cup's organising committee had received more than 100 different balls from all over the world, sent by companies that wanted their product used during the tournament. In the end, ten balls made FIFA's shortlist and were then tested for two hours at the Rasunda Stadium in Stockholm.
This happened in February, many months before the tournament began, and Walter Winterbottom wasn't present, so we'll probably have to dismiss Surridge's bold statement and stick to the traditional version, namely that the FIFA bigwigs ultimately chose ball number 55 and that this happened to be the model from Angelholm.
Still, none of the balls used in 1958 carried a trademark or letters, let alone a logo, and since there were three differently coloured models ... well, who knows? Maybe Mr Winterbottom casually rolled the odd Cobbler onto a Swedish pitch without anyone noticing, figuring it might give him an advantage to have, so to speak, British balls?
Dortmund, however, definitely did use the Cobbler. On photos taken during the 1976-77 season you can clearly make out that uncommon flying object, the Surridge ball.
I wonder how much of an advantage this may have been for Dortmund, the fact that visiting teams had to adapt to an unusual - even foreign - ball. Then again, such vagaries of the travelling footballer's life used to be an accepted occupational hazard in the Bundesliga - until the past summer.
Last season, no less than nine different balls were used across the league and teams would regularly equip themselves with a few of the balls favoured by their upcoming opponent, trying to get used to them in the week leading up to an away game.
But now we have the same ball - the adidas Torfabrik, goal factory - at every ground. Many of the players I know hate this particular model with a passion, although they have to refrain from overt criticism, especially if their club happens to be supplied by adidas. But all of the players I know welcome the fact that a uniform league ball has been introduced at last.
I can understand their reasoning, but since I'm not a player I don't have to follow it. I always liked the fact the ball was different from ground to ground. If you want to gain an edge, there are certainly less sporting ways than using a ball the visitors aren't familiar with. Not to mention that it gave anoraks the chance to tell stories about a ball called Cobbler or to dissect details that distinguish one team from another.
There was, for instance, a time when many clubs in the western part of the country used to get their balls from the specialist supplier Derbystar, a company based in Goch, close to the Dutch border, which was the first to use synthetic materials for footballs.
And you'd always immediately identify balls made by uhlsport, a company based near the Swabian Mountains that specialises in goalkeeping gear but has been producing balls since 1970 that tended to have a distinctive pattern.
The market was so diverse because the two most famous German suppliers, adidas and Puma, began as shoe manufacturers and broadened their product lines only gradually. In the meantime, balls came from companies such as the Jakob Kriener Factory, established in 1925 in the small Swabian town Illertissen. Kriener's heavy leather balls were affectionately known as Iller Bombs.
Then there was the Kaspar Berg company in Nuremberg. Local historians love to call it the oldest sporting goods company in the world because it was founded in 1861, but Berg started out as an iron foundry and didn't concentrate on sports until 1910.
Both pioneers are no longer with us. The Berg company folded in 1992, Kriener's Iller Sport in 1998, as family businesses no longer stood a chance against the giant international corporations they were competing with. Medium-sized companies like Derbystar, though, may survive. Last year, it sold more than 800,000 balls, a company record, by "picking up what the big ones leave lying around", as Derbystar's chief executive recently put it. However, although the company is still the official supplier of the Dutch Eredivisie, its balls are now - thanks to the omnipresence of Torfabrik - almost as rarely sighted in Germany as, say, the Surridge Cobbler.
And that's a tad sad. After all, it was none other than the great Oliver Kahn who, following a defeat away at Schalke in 2003, demanded: "Balls! We need balls!" Please note that he was using the plural form.