Thanks for asking, this is a question I get asked about a lot.
First I would like to tell you a little bit more about letterpress and the printing presses I work on.
I operate 4 different presses, but I mostly use two of them for printing wedding stationery and other custom letterpress work. One is a table top press and is hand operated, I actually feed each individual piece of paper into the press one by one and then operate the lever by arm to close the press and create the impression on the paper. The other press is foot operated, as with my table top press I hand feed each piece of paper into the press, the difference with this larger printing press is that the press is operated by a treadle (think sort of like a bike pedal). I operate the treadle to make the press close, transferring the ink onto the paper and creating the lovely impression letterpress is so well loved for.
Each of my presses can only print one colour at a time, if you can imagine your invitation being printed and it has two colours, I start by inking up the press in the first colour and then hand feed each of your invites one by one through the press to print them, this is the first colour done. I then clean all the ink off the press and let the first colour of your invites dry.
Now time for your second colour, I apply the second ink colour to the press and again hand feed each of your invites through the press to print them in the second colour. At the end of this process your invites are looking pretty special, but don’t forget I have to clean the press again!
Now lets take you back a step to the design process, when you have a two colour invitation I have to create your lovely custom design and the ‘split’ it in two. I have to keep all the parts of your design that will print in the first colour as a separate design and then all the parts that will print in the second colour as another separate design. This can be tricky as I have to ensure both designs will align in the final printed piece, that I don’t miss anything or have any pars that overlap.
I then send the two parts of your design away to be made into photopolymer printing plates, one for each colour. These plates are a very important part of the printing process and what I print from, they are attached to the (platen) inside of the press, the press rollers will apply a thin layer of ink to the raised parts of the printing plate. Then as I operate the press, by hand or foot, the press closes on an individual invite and a layer of ink is applied to that piece of paper.
So as you can see two colour letterpress printing is quite a lengthy process requiring lots of hard work, twice the time and twice the care for the printer.
But well worth the effort as a two colour letterpress invitation certainly is beautiful!