Preparing linoleum blocks for printing, not necessarily the way as it should be done, but it is my way and other printers will most certainly have other ideas.
There are two types of linoleum I use. One is the grey battle ship lino which is smooth and can be cut with sharp detail. It has no texture and as such it prints a flat even colour. The other one I use is six mm thick cork linoleum. Because of the cork it shows a texture when printing, even when all care is taken to smooth sand as perfectly as you can. That however looks nice. It is more lively. I make use of either by itself depending on the effect I like to achieve. Also using them in combination while making a multi block print and sometimes also combine them with ten millimeter poplar ply for colour blocks.
As a rule I glue the sheet of linoleum with neoprene glue onto a sheet of between four and six millimetre MDF (or medium as they call it here in France). Immediately after that run it through the press. Trim the edges of the lino neatly. Then the MDF carrying board is varnished with three coats of gloss varnish, also the edge of the lino so water can’t seep into the jute fabric.
Varnishing firstly prevents the MDF from swelling and distorting while sanding the block with water proof sanding paper and water, but also when cleaning and rinsing the block after a printing session. Besides when you make a slip while inking with the brayer it is easily cleaned.
Then comes the sanding. First with a big flat sanding board to even out any bumps. If you don’t do that it will come to haunt you. Then sand with fine waterproof sand paper, also using a smaller hand held cork sanding block and of course water. It will take a while, but in the end there will be a nice smooth surface to work on. If you wipe the block clean from sanding debris and you glance over it then you will see whether a good job was achieved, if not carry on sanding for a bit longer. This preparation is absolutely essential as if you don’t do it you’ll be plagued by uneven printing results and then it’s too late to rectify it and that after you put so much work into it. On the photo you can see the well varnished MDF board, now being protected from water.
After that I make up a mask of three millimetre MDF to fit snugly around the sheet of lino which has been glued to the heavier MDF sheet. The outer dimensions of that sheet are the same as for the entire block.
This mask serves several purposes. It is used to mark out the registration marks. When it is a multi block print, the same mask is used for the other blocks. Because it is not in contact with the block while inking, there is no chance to mark the nice and expensive sheet of paper. It also lies on top of any ink marks of the brayer made on the supporting sheet of MDF. This mask is not varnished so if there are any inadvertently ink marks, they can be easily sanded away.
Also because the mask only just a smidgen lower than the surface of the lino, the pressure is partly taken by the mask while printing which protects the lino from being compressed too much and possibly loose detail.
After the Key block has been cut and the registration marks are in place then I use heavy cartridge paper to make offset prints on the other prepared lino block(s) and or Prepared ten millimeter poplar ply block(s). To that end the key block is heavily inked (way more than normal) and immediately while the ink is still wet the printed sheet is laid upside down onto the other block (in the registration marks!) and run through the press.
For colour blocks, where appropriate, I use ten millimeter poplar ply. It is a bit rough, but it serves the purpose as it is way cheaper than linoleum. Again this sheet has the same dimensions as the lino block assemblage. As the surface is tender try to avoid scratches where you don’t want them, sand it also to a fine finish and make sure the registration is in place before making the offset image on it.
When Printing, after laying the nice paper onto the inked block I lay a piece of cheap news print paper on top of that (to protect the mill board from possible ink blemishes), then a sheet off heavy card board (mill board) on top of that, to even out the pressure and on top of that a sheet of rubber I cut from camping mattresses.
The card board because it is relief printing after all, the rubber to protect the press and even out possible imperfections of the height of the block. While doing a run I change the orientation of the mill board several times or turn it over in order to avoid it being dented in the same place all the time (mill board is not cheap).