Spot Colour

To contextualise spot colour you need to know that the standard in terms of printing inks is CMYK.

From that you can say that spot colours are essentially any non-standard printing ink.
Use of spot colour is usually when something needs to be printed that can not be printed with any of the standard four inks. Other issues to affect the use of spot colour could be price.
Usually spot colours are individually mixed coloured inks which makes them a much flatter texture on the page because the printer doesn't need to mix any colours together on the page to create it.
Spot colour can also be used for varnishes and for metallic colours.

If you assume that every colour needs it's own lithographic plate in a printing job and your design only uses two colours then it would be much more efficient to use spot colours of the two colours. This would only require two plates to be made instead of the four for CMYK.
Accuracy is also an issue, as in the example above then it would be certain that the colour is exactly what was needed which can't be done easily using CMYK.

There are individual spot colour specification companies for use in printing. The standard spot colour classification system in the UK is the Pantone system.

The company have basically identified all these different spot colours and organised and uniquely classified them each with a code. This means that a specific colour can be really easily described.

For example, this colour on the left can be described specifically as PMS (Pantone Matching System) 294 instead of just a darkish blue.








One issue that designers will always have is that computer screens all vary in quality and brightness and contrast so what you see on screen could print out completely differently.
Pantone fixes this problem with the pantone books as shown above because you can find the colour that you want in the book and then use its reference number in any adobe program to get that exact colour when printed no matter what it looks like on screen.

How cans are made

I was interested in finding out how cans are printed after a session looking at the design of the can really close up. It turns out that the cans are printed as the cans are created.
My information on this post has come from the Can Makers website: www.canmakers.co.uk
This is exactly how the can is made and includes the printing as well.

 The first step is to obtain a big reel of aluminium or steel strip that will be used to make the can.

 The strip is lubricated with a thin laer of oil and then a cupping press blanks out thousands of shallow cups of the metal every minute.

 Each shallow cup is then pushed through a series of rings which raises the walls of the can, thins out the metal and irons it out into its final can shape.

 Trimmers are then used to cut off the spare, uneven metal and the offcuts go elsewhere to be recycled.

 The can is then passed through a washer and then dried which works to take out any excess oil from the previous steps.

 The clean cans are then coated with a clear base coat or a coloured base coat depending on the later steps. This helps make a good surface fro printing the design on to.

 The cans then pass through another dryer to dry the base coat properly.

The next step involves the printing which uses a rotary printing process. It is most likely to be flexography based on the metal being used. The printers apply the design in up to 6 colours plus a varnish.

 Varnish is also coated around the base of the cans using a rim-coater.

 The cans go through another drier which dries the inks and the varnish thoroughly.

 The inside of the cans are sprayed with a special coat of protective lacquer. This is done to protect the contents of the can and avoid any erosion.

 The cans go through another oven to dry the inside.

 The cans go through a 'Necker' which pushes in the can walls just above the top and causes the top to flare out. This makes it ready to hold the lid in a later stage.

 Cans are tested in a light tester which can see if there are any holes or cracks in the cans. Any bad cans get automatically rejected.

The finished can bodies are sent to a warehouse and packaged to be sent to a filling plant.





The next steps involve the can lid:

 The end of the cans are made from the same aluminium material as the bodies. 

 The sheet is fed through a machine which stamps out the ends. It can do thousands in a minute. 

 While they are being stamped the machine also curls the edges up into a rim. 

 The end are passed through a machine which then lines the inside of the curl with a compound sealant which will make it water tight. 

 An inspection system uses video feeds to check each can lid properly. 

 Elsewhere the tabs are made from a thinner width of aluminium coil. The can ends are sent through a system of cutters which score them and attach the tabs on top. 

 The final product emerges. 

 The lids are packaged in sleeves and sent out to the filling factory where they will be attached to the bodies aftr filling. 

It is actually quite a complex process which is not really thought about much when drinking a can. Considering the hundreds of millions of cans that are made in each batch it is quite an impressively cheap exercise considering the complexity of the manufacture and the retail price of a single can. 

One thing that stuck out from the process is that it utilizes the same rotary print machinery that I have researched before this. It is also interesting that it uses a hexachrome printing machine and when examining the can in the session I saw that it had 6 colours so this makes sense. 

Pad Printing

Pad printing is essentially the process of printing a 2D image on to a 3 dimensional object rather than a flat one. This done by transferring the image to be printed on to a silicone pad and then on to the object.



This is one example of how the pad printing process can be used to print on a 3D object.
There are a lot of other examples such as these:

Pretty much anything 3D can be pad printed but usually it will only be because there is no other realistic way to print it.

Digital Print

Digital Print is exactly what it sounds like: Printing from a digital source directly onto a type of media.

Digital print will be created using either an Inkjet or a Laser printer. Digital print is more expensive per sheet and also a lot slower than conventional rotary printing which means that it is only really ever used for relatively small print runs.

If rotary printing were used on a small print run then the setting up cost of the machine and of getting the plates created would make the job much more expensive than if digital print was used.

As technology progresses, digital print quality is increasing dramatically and has reached a near perfect quality at large resolutions, making it a suitable 

medium for highly detailed print. As the digital printers develop rapidly we may see digital print making rotary print jobs redundant in the near future.
Digital printers work on a specific set of colours which mix on the page to create the required colour. Unlike rotary print processes, digital print is limited to just these 4 colours. The colours are Cyan, Magenta, Yellow and Key Black.



CMYK


CMYK stands for Cyan, Magenta, Yellow and Key which are the 4 colours that make up every colour in digital print. These colours are effectively blue, pink, yellow and black but with more specific hues.
CMYK is a brilliant way of making a lot of colours because for small jobs it is very cheap and easy in comparison to other printing methods.
The only problem with CMYK is that the gamut is relatively limited compared to all the colours that our eyes can see. Gamut just effectively means a range.
All this means is that there are quite a lot of colours that digital printing can not print.

You can see above that CMYK gamut fills only about a quarter of the visible spectrum. That leaves a lot of colour that can not be printed digitally. 

You can also see the RGB gamut which stand for Red, Green and Blue which are the colours of light that make up colour on screen. Although RGB still cant replicate every colour in the spectrum it is clear that it can make a lot more colours than CMYK can. 

Additive and Subtractive

Additive colour is the process of adding different wavelengths of light (colours of light) together to create new wavelengths. This creates new colours.

This is usually done with RGB colour. When red, green and blue light are mixed they create pure white.

The first additive colour image was created in 1861 by James Clerk Maxwell. He thought he understood how the process worked so he got someone to take a photograph of a tartan ribbon 3 times; Each time with either a red, green or blue filter over the lens. 

He then developed the films and projected each image through a different projector, each projector with the corresponding filter attached and then aligned on a wall. 

When aligned it showed this full colour additive image of the tartan ribbon:

Subtractive Colour

Subtractive colour is basically the opposite. It is the mixing of inks and dyes and paints to make colour and in the case of digital print it means CMYK. Colours are still mixed to create other colours, but in the instance of subtractive colour the light wavelengths are subtracted (or absorbed) instead of added to change the colour. 

The easiest way to differentiate is that additive colour starts with darkness and creates light and subtractive colour starts with light and goes together to make darkness.

Flexography

Flexography is another Rotary Print process like Offset and Rotogravure.
It is a Relief print process which means that parts of the plate (Or wood or plastic sheet) are cut away.
This makes it very similar to intaglio, but in relief print it is the parts that are left behind that make the print rather than the grooves which have been created by cutting away material.
Here is an example of a wood block that has been carved ready to print with.

This style of wood block printing originated in East Asia a very long time ago and is still a commonplace printing method in China and Japan. The earliest examples of wood block printing date back as far as 220 AD. The traditional style is often printed on to fabrics and considering the manual printing can be incredibly detailed. 

Flexography is almost exactly like the description above except the plate is a flexible polymer material so that it can wrapped around a roller and used in the same way as other rotary printing processes.

Flexographic printing can produce a greater range of inks than lithographic printing  and is good at printing on a variety of different materials like plastics, papers and foil most specifically in packaging. These are some of the products that flexographic printing can produce: