By understanding the processes in which MTG cards are made, we can understand how the errors we see in our packs come to exist.  Misprints can happen at any stage of card production so this simple overview will give you a better idea of the step by step processes that go into production, and what types of errors happen at each of those stages.

Step 1: Card Design (WotC/Printer)

The very first step in the production of Magic cards is designing them. This doesn’t only include the core design of the card, but also new mechanics that can change how cards have traditionally looked (Planeswalkers, DFC, and meld for examples), new card/frame layouts, and special treatments. When desinging a significant change to the template or materials of a card test prints are developed and printed to see if they're what WotC wants for their new products.  Test prints are made for things like new card frames, new foiling methods, holostamps, and more.  Check out the librarities website for a list of most known test prints.

Step 2: Layout (WotC/Printer)

Once the cards have been designed, it’s time to prepare them to be printed. This includes putting all the pieces of a card into a single file (text, frame, mana cost, collectors number, art, etc) to make the card for print. Once all the cards have been compiled they are then arranged into a sheet layout for print. Sheet layouts are depedant on the number of cards being printed in a rarity, the product being printed, and many other factors. When you don’t have enough cards to fill a sheet, fillers can be added to the sheet. Every single printing (all languages, card versions, foil/non-foil, etc.) will need its own unique sheet layout. This is where the source of all human error misprints lives.  This is largely due to the many printing variants that need to get designed. We'll often see minor (or major) mistakes between these variants.  For example; Traditional Chinese Foil M15 planeswalkers might be missing their loyalty counter number or Italian 5th Edition Breeding Pits have no casting cost, etc.  For a list of all documented (there are many not currently listed) human error misprints check out this link, and this one too.

Step 3: Cardstock Production & Selection (Paper Manufacturer)

There are a ton of different types of cardstock used across all MTG products. These various cardstocks are not produced by WotC or the printing facility, but specifically by a paper manufacturer. Embedded objects and other cardstock errors happen during this production process. The main variations of cardstock involve foiling and the type of core the card has. For cores we have seen the traditional blue core, black cores, and no core (aka token stock). For foiling we have seen non-foil, foil on one side, and foil on both sides as well as different foil variations.

Step 4: Plate Production (Printer)

In traditional offset lithographic printing metal plates need to be manufactured for each layer of color to be printed. Each plate is etched with the image of the layer that it will print. The process of converting a sheet layout into its respective color layers is known as raster image processing, or RIP for short. These plates will be attached to a cylinder that makes contact with the ink cylinder. This is how the image will eventually get transferred to the paper (by the offset cylinder). Any damage to the plate will affect the print run it is used for. The hairy Runesword is a good example of a scratched plate.

Step 5: Printing (Printer)

Magic cards are printed in a process called offset printing*.  In offset printing each of the 4 printing colors (CMYK**) are printed separately from one another.  Additionally, there’s a 2nd layer of black specifically for the card’s text and borders. Each color being printed separately gives us room for errors to happen at each color.  Single or multiple color channels can have the incorrect ink consistency, have something obstruct the channel (like a splotch), or have the rubber rollers not properly cleaned between passes resulting in all sorts of neat misprints, which I cover in the beginners guide to misprints.  Here's a video that describes the offset printing process:

*Note: The majority of MTG cards have been printed with traditional offset lithographic presses. However, several products recently (such as Jumpstart) have been produced with Digital Offset Presses. Rather than use traditional metal plates, lasers with varying levels of positive charges create images on a Printing Image Plate. When this plate comes into contact with negatively charged inks, the inks adhere to the plate, which is then transferred to the offset cylinder. This process of using charged inks has led to some errors specific to Jumpstart only.

**Note:  Foil cards get an extra layer of ink applied to them before the CMYK layers called the underprinting layer.  The underprinting determines which parts of the card allow the foil to show through and which parts are masked.  These masks are created by layout artists and are greyscale representations of which parts of the card should show how much foil.  White represents no underprinting (100% foil) and black represents full underprinting (0% foil).

Step 6: Finishes and Press Coats (Printer)

After the sheet has been printed it gets finished with an application of a clear UV cured lacquer. This lacquer will protect the card from play wear, determine the final texture and finish of the card, and add a little more structural rigidity. Some modern card treatments are applied prior to the final clear coat such as etched foiling and other similar effects. There are also effects that are applied using thicker layers of the varnish to give a texture to the surface of the card. Most of the types of errors that can happen with ink can happen with the varnish layer too, but they’re generally harder to see and not as desired by misprint collectors.

**Note: The textured finish of poker cards that enables easy shuffling is called a Linen Finish and is a clear coat effect created during the curing of the varnish.

Step 7: Stamping (Printer)

Before the sheets are cut into individual cards any stamping will be applied to each card. This could be the holostamp for rares, promotional stamps, or prerelease & other date stamps. These stamps are stamped with a process called hot pressing which applies foil to the card surface using a cutout die, heat, and pressure. The result are foil stamps which are fused to the surface of the card and embedded with a tactile feel.

Step 8: Cutting (Printer)

Once the sheet is printed, stamped, and varnished it's time to make cards out of it.  This is done in two separate cuts.  The first cut divides the sheet into rows. The next cut takes those rows and makes vertical cuts to divide them into individual cards. It should go without saying that if the sheet gets a little shifted prior to either cut, that this is how we get miscuts.  If the row of cards shifts diagonally before the 2nd cut, you’ll get cards in the shape of parallelograms instead of rectangles.

Step 9: Corners (Printer)

When the cards are cut from the sheet, the corners are still square.  The cards are put through a die press which neatly cuts the corners.  Interestingly enough, you can tell which side of the cards are facing upwards when the die press makes the cuts by taking a close look at the corners. If the stack of cards are skewed when they are put in the corner rounding machine, it’s possible that some of the corners will be at an angle where they miss the rounding die entirely. This is how we get cards with 1 or more square corners.

Step 10: Collation & Packaging (Printer/Finishing Facility)

The last step of the process is packaging the cards into sealed products so they can be shipped out and sold to you.  This includes organizing them into packs of commons, uncommons, and rares as well as wrapping them in boosters and packaging them into boxes.  In the process of sealing boosters closed, cards can get caught in the heat press and get crimped.  Also, sometimes there are issues with the booster foil.  There have been "miscut" booster packs, as well as 'double printed' boosters, and even boosters with a tape-like covering that have been found in booster boxes. Sometimes this process is done at a separate facility than the printing facility.

I hope you've enjoyed this article on the manufacturing of MTG cards from a misprint collector's perspective.  It's important to note that magic has been printed for over 30 years.  In that time the specifics of the technology and processes have changed.  Machines have been updated, and new print facilities around the world are now being utilized.  There's no one way that all magic cards have been printed, but the general principles have stayed the same (for now).  The key thing to continue to look for are new things in magic.  Think about how the print process has to change if a new unique mechanic alters our perception of a normal magic card.  There's always opportunities for new types of misprints!

Additional Resources:

How it’s Made featuring Cartamundi, the original printer of MTG:

Print Ninja Printing Academy

The Anatomy of a Card

PrintWiki.org

Building a Card

Playing Card Coatings