Know­ing that all of your mat­ter to be print­ed has to be locked togeth­er in a met­al frame (the chase) leads to some impor­tant ques­tions, the pri­ma­ry one being: how can I make sure that every­thing will be lev­el and main­tain its struc­ture?  This prac­tice is called ​‘lock­up’.  Where lock­up is weak, it allows things to move with­in the forme and caus­es inac­cu­ra­cies.  In addi­tion, loose mate­r­i­al (like spaces) can work up from the forme to touch the print­ed page.  This leaves a black square mark between words where the spac­ing mate­r­i­al has been inked and print­ed.

In longer-run jobs the impact of ris­ing spaces is mag­ni­fied: if a space is loose and can work up on each impres­sion, a move­ment of just 0.001″ per impres­sion will cause the space to print on the page after just 500 impres­sions.  In the world of com­mer­cial, high-vol­ume let­ter­press this could be a mas­sive prob­lem.

The stan­dard warn­ings appear here about clean­li­ness and accu­ra­cy.  Make sure the bed of your press is clean, but also the back of the forme.  If need­ed turn the chase over and rest it on some paper on the stone.  Brush the back of the forme to make sure no debris will force a move­ment when it’s put in the bed of the press.

Ensure your mate­ri­als are accu­rate: wood fur­ni­ture will absorb some of the inac­cu­ra­cies of your forme, but can also be affect­ed by mois­ture and warp­ing.  Even the ini­tial cut­ting of fur­ni­ture could be incor­rect.  Most print­ers moved from wood to met­al (alu­mini­um) or formi­ca (Resalite) fur­ni­ture from the 1950s.  Some wood­en fur­ni­ture is still need­ed to absorb some of the pres­sures in a chase.  Make sure you peri­od­i­cal­ly check that your chas­es are true by rest­ing them on your impos­ing sur­face and see­ing if the ​‘rock’.

Tack­le lock­up in sec­tions: by mak­ing sure each line is prop­er­ly spaced; and then lock­ing up work sec­tion-by-sec­tion you will find and cor­rect errors much more quick­ly than by dis­cov­er­ing an error just before you go to press.

Dur­ing print­ing any move­ment of the machine or vibra­tion will con­tribute to spaces ris­ing, so the whole machine should be clean.

There is some spe­cif­ic advice for some types of mat­ter —

• Mono­type Mat­ter
  Should have most pres­sure for lock up applied at the top and bot­tom of the forme because the spac­ing between words is sel­dom as good as hand com­po­si­tion.  When print­ing on a cylin­der press it should be set par­al­lel to the cylin­der because top-bot­tom move­ment would be min­i­mal
• Linotype/Intertype/Lud­low Mat­ter
  Should be checked for accu­ra­cy of the slug, espe­cial­ly where the foot of the slug is small­er than the head.  In lock­ing up this would lead to a bulge as the feet of the slugs meet each oth­er and the head of the slug remains in place.  This can be avoid­ed by using thin paper or cop­per strips at the foot of the slug per­haps 0.002″ thick.  An alter­na­tive is to use wet blot­ting paper that will dry to cre­ate a sol­id block.  In print­ing on a cylin­der press this should be set at right angles to the cylin­der as left-right move­ment will be min­i­mal
• Blocks
  These should be checked to ensure they are true.  Where they need some fur­ther lead­ing on one side, this should be tacked in to place

Final­ly where a forme can­not be cor­rect­ed there is a very severe option: mix resin and meths.  Pour this on the forme and brush it away from the face of the type.  The whole forme will now be a sin­gle, sol­id mass.  At the end of print­ing, soak this in hot water to dis­solve the resin and diss the type.