Production Methods

Book coverAs an intro­duc­tion to tra­di­tion­al print­ing tech­nolo­gies as in use dur­ing the twen­ti­eth cen­tu­ry How it Works: Print­ing Process­es by David Carey and illus­trat­ed by B.H. Robin­son, © Lady­bird Books Ltd, 1971 is repro­duced here by kind per­mis­sion of the pub­lish­ers.

The Main Printing Processes

PhotogravureThere are sev­er­al dif­fer­ent print­ing process­es, and one or more vari­a­tions of each. Each process has its own spe­cial advan­tages and lim­i­ta­tions.

The three most impor­tant meth­ods are:

  • Let­ter­press print­ing which is car­ried out from a raised sur­face.
  • Lith­o­g­ra­phy, or litho, to use its more com­mon name, involves print­ing from a flat or very slight­ly recessed sur­face.
  • Pho­togravure, nor­mal­ly short­ened to gravure, is print­ing from a recessed sur­face. This process is also known as intaglio print­ing. (The word comes from the Ital­ian and means ‘to cut into’.)

Setting & Assembling the Type

Setting the Type

When mov­able type was first invent­ed in the mid-six­teenth cen­tu­ry, all the sep­a­rate pieces were kept in two cas­es, one above the oth­er. The upper case always con­tained the cap­i­tal let­ters and the low­er case held the small let­ters. Cap­i­tals thus became known as upper case let­ters and the small type as low­er case, and this ter­mi­nol­o­gy is used in print­ing even today.

Composing stickType was always set by hand, one let­ter at a time being placed in a nar­row tray, known as a com­pos­ing stick, which was held in the oth­er hand. By mov­ing a slide along the tray and fix­ing it in the desired posi­tion, the lines of let­ters could be set to a pre­cise width. Most type-set­ting today is done by machines which do the job very quick­ly, but the com­pos­ing stick is still used when a small amount of set­ting has to be done, such as dis­play head­ings, for cor­rec­tions or when there are a num­ber of dif­fer­ent sorts and sizes of type to be set.

The man who sets the type and com­pos­es the page is called a com­pos­i­tor. Type let­ters are made the wrong way round so that they will repro­duce the right way when print­ed onto paper. Hold some print­ed mat­ter up to a mir­ror and you will get a compositor’s eye view of the type.

Mechanical Typesetting

Machines for set­ting and cast­ing met­al type have been in use since the late nine­teenth cen­tu­ry. There are two main kinds used today: Mono­type by which the char­ac­ters are cast indi­vid­u­al­ly, one at a time, and Lino­type which casts a com­plete line in the form of a type slug.

Although the two machines are real­ly quite dif­fer­ent in oper­a­tion they both have key­boards con­tain­ing all the nec­es­sary upper and low­er case char­ac­ters, fig­ures, punc­tu­a­tion marks, spaces and so on. The oper­a­tor press­es the appro­pri­ate keys on the key­board and this sets the var­i­ous mech­a­nisms in motion.

Apart from the nor­mal type keys, the key­board also includes what are known as jus­ti­fi­ca­tion keys. Usu­al­ly on a print­ed page, the lines of type end even­ly, each line being of exact­ly the same length. In oth­er words, the lines are jus­ti­fied. When the key­board oper­a­tor has near­ly reached the end of the line he is set­ting, a jus­ti­fy­ing indi­ca­tor tells him what space is left. He must then decide whether he can com­plete the last word or whether the line has to be jus­ti­fied. If the word is too long, he press­es a jus­ti­fi­ca­tion key and this adjusts the spaces between the exist­ing words so that the line is set to the exact mea­sure required.

The Monotype Process

Monotype keyboardOper­at­ing the key­board of a Mono­type machine does not imme­di­ate­ly pro­duce let­ters and words. What it does is to cause a suc­ces­sion of holes to be punched in a roll of paper mount­ed above the key­board, each char­ac­ter being rep­re­sent­ed by a dif­fer­ent arrange­ment of two holes.

Just below the paper is a series of air-oper­at­ed punch­es. Every time a key is pressed two jets of com­pressed-air are released, two valves open and the appro­pri­ate two punch­es are made to per­fo­rate the paper. This hap­pens for each char­ac­ter in turn until the key­board oper­a­tion is com­plete. The paper roll is then removed and trans­ferred to the type cast­er, which is a sep­a­rate machine and the one that actu­al­ly makes all the pieces of type. Its func­tion­ing is entire­ly con­trolled by the per­fo­ra­tions in the paper.

Monotype casterA pat­tern, or matrix, of every piece of type like­ly to be need­ed is con­tained in a matrix case which is put in place on the cast­er. As the per­fo­rat­ed paper is fed though the machine it pass­es over a series of com­pressed-air pipes. Where every two per­fo­ra­tions occur, jets of air are allowed to pass through. These raise pins which lim­it the move­ment of the matrix case, bring­ing the matrix for that par­tic­u­lar char­ac­ter over a small hol­low, or mould. Molten met­al is inject­ed into the mould; it sets imme­di­ate­ly and a cast impres­sion of the type is made.

The Linotype Process

LinotypeUnlike the Mono­type sys­tem, which has a sep­a­rate key­board and cast­er, the Lino­type method com­bines both func­tions in the one machine. It is per­haps the more pop­u­lar of the two, espe­cial­ly where a large amount of type-set­ting is need­ed, as in news­pa­pers for instance.

Instead of a roll of paper above the key­board, the Lino­type machine car­ries a large matrix mag­a­zine (1). When a key is pressed the required matrix is eject­ed onto a con­vey­or which takes it to an assem­bly box where it is quick­ly fol­lowed by oth­er matri­ces, shown as arrows on the illus­tra­tion, to make up the words of a com­plete line (2). At the end of each line the key­board oper­a­tor moves a lever and the box of matri­ces pass­es in front of a geared wheel (3) car­ry­ing a num­ber of moulds. The rota­tion of the wheel is timed so that as each line of matri­ces arrives, one mould will fit over it. Molten met­al is pumped into the mould, and the line is cast in a slug of type which is eject­ed onto the gal­ley (4). The next mould on the wheel fits over the next line of matri­ces and so the process is con­tin­ued in a suc­ces­sion of rapid, cast­ing oper­a­tions.

The sup­ply of matri­ces in the mag­a­zine is lim­it­ed, so there is a device incor­po­rat­ed in the machine which sends each matrix back to the mag­a­zine to be used again as soon as the type has been cast.

Film Setting

FilmsetterThere is a third method of set­ting type and that is by means of pho­to­graph­ic film. It is a process that has gained in pop­u­lar­i­ty and use over the last few years. There are sev­er­al makes of machine avail­able, some oper­at­ed elec­tron­i­cal­ly, but the one in most gen­er­al use at the present time is the Monopho­to Film­set­ter.

The machine retains some of the fea­tures of the Mono­type sys­tem, described ear­li­er, in that the oper­a­tion of a key­board caus­es holes to be punched in rolls of paper tape. How­ev­er, instead of the nor­mal matrix case and type cast­er, the sys­tem uses neg­a­tive images of the type on pieces of film, con­tained in a film matrix case, which can be select­ed and repro­duced pho­to­graph­i­cal­ly.

The paper tape is fed past air pipes as before, and the arrange­ment of holes, allow­ing air to pass through, con­trols the selec­tion of the pieces of type film in the film matrix case. A beam of light is pro­ject­ed through the select­ed matrix and a pos­i­tive image of the type is pho­to­graph­i­cal­ly print­ed on to a sheet of film mate­r­i­al con­tained in a drum. The pho­tograph­ing is done through an arrange­ment of lens­es and prisms, the adjust­ment of which enables the type image to be enlarged or reduced as required. As with type cast­ing, film set­ting is car­ried out at quite fast speeds. The result­ing film can be used for mak­ing let­ter­press print­ing blocks or lith­o­graph­ic print­ing plates.

Galleys and Proofs

GalleyWhen each line of type has been pro­duced by a type cast­er, it is eject­ed into a long, shal­low, met­al tray placed at the side of the machine. This tray is known as a gal­ley. An impres­sion, or proof, of the type in the gal­ley is next print­ed on to paper. The paper is usu­al­ly in long strips sim­i­lar to the shape of the gal­ley, and a proof of this kind is called a gal­ley proof.

The gal­ley proof pro­vides a first oppor­tu­ni­ty for the type-set­ting to be checked visu­al­ly, and the per­son who does this job is the proof­read­er. He is a very impor­tant mem­ber of a print­ing organ­i­sa­tion and is skilled in find­ing any errors which might have been made by the key­board oper­a­tor, and any faults in the type itself. He checks the proof against the orig­i­nal text, or copy, from which the type was set and makes sure the set­ting exact­ly fol­lows the orig­i­nal, let­ter by let­ter and word by word. Any errors he finds are not­ed with spe­cial marks so that they can be cor­rect­ed by the com­pos­i­tor.

After gal­ley proof­ing, the long strips of type are split up into page lengths and a fur­ther page proof is tak­en to make sure the orig­i­nal mis­takes have been cor­rect­ed and no addi­tion­al ones have occurred.

Formes and Furniture

Forme and furnitureThe pages of a book are not print­ed sep­a­rate­ly, one at a time, but on larg­er sheets of paper car­ry­ing four, eight, twelve or more pages on each side. The areas of type must be so arranged that when they are print­ed, and the sheets fold­ed, the pages fol­low one anoth­er in their cor­rect sequence. The arrang­ing of the type in this way is known as impo­si­tion.

Impo­si­tion for let­ter­press print­ing is car­ried out on a big cast-iron table with a per­fect­ly flat top (a stone), and the var­i­ous areas of type are posi­tioned with­in a steel frame known as a chase. Fur­ni­ture, in the form of pieces of met­al or wood, is insert­ed between the page areas of type and between the type and the chase to keep them the cor­rect dis­tance apart. Steel wedges, or quoins, are then tapped into posi­tion between the fur­ni­ture and the chase, and final­ly tight­ened up by means of a key until noth­ing can move. This com­plete and now sol­id assem­bly of chase, type, fur­ni­ture and quoins is known as the print­ing forme. After a last proof has been tak­en, as a final check, it can be put on a let­ter­press machine for print­ing.

Reproducing illustrations

Reproducing Illustrations â-” Letterpress Process

Reproducing illustrationsSo far we have dealt with the basic facts about mak­ing, set­ting and impos­ing type, but what if the print­ed book, news­pa­per or mag­a­zine needs to include illus­tra­tions? This requires an entire­ly dif­fer­ent tech­nique which, for let­ter­press print­ing, is known as process engrav­ing or block­mak­ing.

In print­ing terms there are just two kinds of illus­tra­tions, line and half-tone. With line blocks the print­ing sur­face pro­duces a sol­id colour on the paper with­out any gra­da­tions of tone. In oth­er words it is sim­ply one colour or white with­out any shades of colour between. This kind of block prints well on even the poor­est qual­i­ty paper and is suit­able for repro­duc­ing type-mat­ter and pen-and-ink draw­ings.

Half-tone blocks are used to repro­duce from sub­jects such as pho­tographs or wash draw­ings in which the tones vary through­out the illus­tra­tion. If you look through a mag­ni­fy­ing glass at a pho­to­graph in a news­pa­per or mag­a­zine, you will see that it is bro­ken up into a mass of dots. These dots are larg­er and more close­ly-packed in the dark areas, and are small­er, more wide­ly-spaced in the light areas. Lat­er in this book we shall learn how this dot for­ma­tion is achieved. Gen­er­al­ly speak­ing, half-tone blocks repro­duce bet­ter on good qual­i­ty paper, although the screen plays an impor­tant part in this.

Making a Line Block

Line blockThe draw­ing from which a line block is made is mount­ed on a copy board which is bright­ly and even­ly lit by arc lamps. Fac­ing the copy board is a large process cam­era which is mount­ed on rails so that it can be adjust­ed back­ward and for­ward to obtain the cor­rect focus and to enlarge or reduce the image. A neg­a­tive image (1) is pro­duced and this is pho­to­graph­i­cal­ly print­ed down onto a met­al plate, nor­mal­ly of zinc alloy treat­ed with a spe­cial, light-sen­si­tive solu­tion.

Neg­a­tive and plate are fixed in a vac­u­um frame (2) from which all air is exclud­ed to ensure per­fect con­tact. Both are then exposed to a bright light for a pre-set time. Where the light pen­e­trates the lighter areas of the neg­a­tive and reach­es the solu­tion, it hard­ens slight­ly. The remain­ing area of the solu­tion remains soft and is after­wards washed away with water (3). On the zinc plate there is then an image match­ing that of the neg­a­tive, the light areas of the neg­a­tive show­ing as hard­ened solu­tion on the plate, and the dark areas as bare zinc alloy (4). The hard­ened solu­tion is then fur­ther hard­ened by heat which forms an acid-resist­ing enam­el over it.

The plate is then placed in an etch­ing machine con­tain­ing a bath of acid. Motor-dri­ven pad­dles splash the acid onto the plate, and the light, unpro­tect­ed areas are etched away, leav­ing the enam­elled met­al print­ing sur­face raised above the sur­round­ing met­al. From this a proof (6) can be tak­en.

Making Half-tone Blocks

Half-tone blockHalf-tone blocks are pro­duced in an essen­tial­ly sim­i­lar man­ner to line blocks, the sub­ject being pho­tographed and a neg­a­tive print­ed down onto a light-sen­si­tive solu­tion pre­vi­ous­ly applied to a met­al plate, which is then etched in acid. In this case, how­ev­er, the met­al is usu­al­ly cop­per and the vary­ing tones of the sub­ject have to be repro­duced by means of dots.

In fact, the sub­ject is pho­tographed through a glass screen. This con­sists of a cir­cu­lar piece of opti­cal glass on which are drawn a great num­ber of black lines cross­ing each oth­er at right angles and form­ing a fine grid. Because the sub­ject is pho­tographed through this screen, the lines of the screen appear on the neg­a­tive. They appear dense and heavy in the dark areas and as thin lines in the light areas. The neg­a­tive is print­ed down onto the sen­si­tized plate, the soft areas of the solu­tion (match­ing the dark areas of the neg­a­tive and the screen lines) lat­er being washed away and leav­ing the hard­ened areas. When the plate is etched, the thin lines of the screen lose their reg­u­lar shape and become the raised dots of the half-tone block.

Screens vary in the num­ber of lines drawn across them A greater num­ber of lines gives a fine screen, less lines gives a coarse screen. Screens of 55, 65, 85, 100, 120 and 133 lines to the inch are com­mon. Poor print­ing sur­faces need coars­er screens.

Engraving for Colour

Colour engravingPrint­ing illus­tra­tions in their nat­ur­al colours, instead of black and white, is done by what is called the four-colour process. In oth­er words all the colours of the sub­ject have to be pro­duced by four coloured inks only, name­ly- yel­low, red, blue and black.

Half-tone colour blocks — a sep­a­rate block for each colour — are made in the same way as a black and white one except that a light fil­ter is placed in front of the cam­era lens so that only one colour is pho­tographed at a time. A vio­let fil­ter is used to iso­late yel­low for the yel­low neg­a­tive, a green fil­ter for the red neg­a­tive and a red fil­ter for the blue neg­a­tive. A com­bi­na­tion fil­ter is used for black, which is real­ly an extra print­ing to give depth and con­trast to the illus­tra­tion.

To ensure that the four dif­fer­ent coloured dots do not print one on top of the oth­er, the screen is rotat­ed a giv­en num­ber of degrees for each colour expo­sure and the dots print in a cir­cu­lar pat­tern. Where nec­es­sary the white paper shows through the colours to pro­duce high­lights and oth­er bright areas.

When print­ing by the let­ter­press four-colour process, yel­low is usu­al­ly the first colour on, fol­lowed by red, blue and black, in that order. The illus­tra­tions on the oppo­site page show the yel­low, red and blue print­ed sep­a­rate­ly, and the effect pro­duced by print­ing them togeth­er with the black.

Electronic Engraving

Electronic engravingAs with almost every oth­er tech­no­log­i­cal process, elec­tron­ic equip­ment is being intro­duced more and more into block­mak­ing. We will there­fore take a quick look at a machine called the Vario-Klischo­graph which makes blocks auto­mat­i­cal­ly with­out neg­a­tives and with­out pho­to­graph­ic print­ing onto met­al.

The sub­ject, a draw­ing or pho­to­graph, is held by vac­u­um onto a glass-topped table and the plate to be engraved is sim­i­lar­ly secured to anoth­er table. An elec­tron­ic scan­ner ‘reads’ the sub­ject by sweep­ing a spot of light back­ward and for­ward across it. The light is reflect­ed back into the scan­ner from where it is trans­mit­ted onto pho­to-elec­tric cells which turn the light spots into tiny elec­tric impuls­es. Greater reflec­tion is pro­vid­ed by the pale areas of the sub­ject, giv­ing a larg­er impulse. Less reflec­tion is received from the dark areas which pro­duce a cor­re­spond­ing­ly reduced impulse.

The elec­tric impuls­es are used to oper­ate an engrav­ing head mount­ed over the plate. This engraves dots into the plate, the size of the dots vary­ing accord­ing to the light and dark areas of the sub­ject as read by the scan­ner. In this way the engrav­ing on the plate becomes a faith­ful repro­duc­tion of the sub­ject pic­ture. For colour engrav­ing, the light spots are passed through appro­pri­ate­ly coloured fil­ters and the plates are rotat­ed for each colour as with the glass screen.

Stereos and Electros

StereosIt is some­times more con­ve­nient to print type mat­ter from a block rather than from the type itself, and it may also be nec­es­sary to make dupli­cate copies of these blocks. Dupli­cates of both type blocks and line blocks are known as stere­os and the process of obtain­ing them is stereo­typ­ing. The method is quite sim­ple. The type forme or block is placed in an elec­tri­cal­ly heat­ed mould­ing press and a sheet of plas­tic is laid over it. The press is oper­at­ed at a pre-set tem­per­a­ture and tim­ing, and an impres­sion of the type or block is tak­en by the plas­tic sheet. This now becomes a mould, or matrix, into which molten met­al is poured and the stereo is made. Papi­er Mâché is some­times used for matri­ces and, quite often, stere­os are made from plas­tic or rub­ber.

Copies of half-tone blocks can also be made. These are pro­duced by a process of elec­trotyp­ing and the copy is known as an elec­tro. An impres­sion of the half-tone block is tak­en in a mould­ing press. The mould­ing mate­r­i­al can be lead, but plas­tic Vinylite is more com­mon. The mould is then sprayed with an elec­tric­i­ty-con­duct­ing solu­tion and put into a bath of cop­per sul­phate in which is sus­pend­ed a cop­per plate. A low-volt­age cur­rent is passed through the bath and, by a process of elec­trol­y­sis, cop­per is deposit­ed from the plate onto the mould. The mould is removed and the hol­low back of the elec­tro shell is then filled with molten met­al to give it strength.

Machine printing

Letterpress Machinery

Rotary pressThere are two basic kinds of let­ter­press print­ing machine, although there are many makes and vari­a­tions of each kind. There is the flat-bed machine which prints from a forme or some oth­er hor­i­zon­tal mount­ing of type and blocks, and the rotary machine in which the print­ing sur­face is made in the form of a wrap-round plate fit­ted to a rotat­ing cylin­der. Very large ver­sions of the rotary print­ing press are used in the pro­duc­tion of news­pa­pers.

On flat-bed machines the print­ing forme is fixed to a rec­i­p­ro­cat­ing forme bed which trav­els back­ward and for­ward. At one end of its trav­el it runs under ink­ing rollers which spread the ink even­ly over the print­ing sur­face. At the oth­er end it comes into con­tact with the paper onto which the inked impres­sion is trans­ferred.

Paper is stacked in sheets at the feed­ing end of the machine and is picked up by suc­tion cups, one sheet at a time. It grav­i­tates down a feed­er board and on to a rotat­ing cylin­der. As the lead­ing edge of the sheet reach­es the under­side of the cylin­der it is pressed into con­tact with the inked forme and then car­ries on round the cylin­der before detach­ing itself and mov­ing down a deliv­ery board on to the stack of print­ed sheets.

The process out­lined on the pre­vi­ous page is sim­pli­fied in order to give the essen­tial details rather than a descrip­tion of a par­tic­u­lar machine. One point not men­tioned is that imme­di­ate­ly after a sheet of paper is print­ed a fine pow­der is sprayed on the print­ed sur­face to pre­vent set-off This hap­pens if wet ink on one sheet is allowed to mark the under­side of the fol­low­ing sheet in the stack.

Colour print­ing can be done one colour at a time as described, the oth­er colours being added by send­ing the paper through the same or anoth­er machine again for each of the remain­ing colours. Two-colour and four-colour machines are often used; these print two or four colours in quick suc­ces­sion as the paper is fed through a series of cylin­ders and over the appro­pri­ate num­ber of print­ing plates. Of course, when the paper has been print­ed on one side it must go through the machines again so that the reverse side can be print­ed.

On rotary news­pa­per press­es, there are two cylin­ders car­ry­ing the curved print­ing plates and two con­trol­ling the paper. The cylin­ders rotate one against the oth­er and the con­tin­u­ous web of paper runs between. Each pair of cylin­ders prints one side of the paper which is thus print­ed on both sides at once.

The Lithographic Process

Litho print­ing is done from a very thin met­al plate, usu­al­ly made of zinc and alu­minum, which can be bent to fit round a print­ing cylin­der. Because this form of print­ing uses a flat, or very slight­ly recessed sur­face, a means has to be found of con­fin­ing the ink to the image areas of the plate and keep­ing it away from the non-print­ing por­tions. With­out some such method the rollers would sim­ply cov­er the whole plate with ink and the result would be a ter­ri­ble mess.

The sys­tem depends on the actions of two nat­ur­al ene­mies â-” grease and water. A greasy sub­stance is applied to the areas to be print­ed, and the non-print­ing areas (which have a very fine­ly-grained sur­face) are damp­ened with water. A very fine film of water is retained by this grained sur­face. The greasy print­ing ink adheres to the greasy image but is reject­ed by the water on the damp­ened part of the plate which there­fore remains clean and does not mark the paper.

Photolitho and Offset-litho Printing

Web offsetLitho print­ing plates are pro­duced pho­to­graph­i­cal­ly by mak­ing a neg­a­tive image of the sub­ject; it might be type­mat­ter or illus­tra­tions or both. The illus­tra­tion neg­a­tive is then pho­tographed through a screen and a pos­i­tive screened image is pro­duced on film. Alter­na­tive­ly, the pos­i­tive film can be pro­duced by the Vario-Klischo­graph described (see Elec­tron­ic Engrav­ing) and oth­er sim­i­lar machines. This film is then exposed onto a light-sen­si­tive plate. The print­ing image thus pro­duced may be left flat or light­ly etched into the met­al with acid. Unlike a let­ter­press block, the image on a litho plate is the right way round. This is because the plate does not print direct­ly on the paper as in let­ter­press. The impres­sion is first trans­ferred, or off­set, onto a cylin­der car­ry­ing a rub­ber blan­ket, and from there onto the paper. This process is known as off­set-litho and is the one now uni­ver­sal­ly adopt­ed. It gives a soft­er appear­ance to the print­ed pic­ture than let­ter­press, it can be used on less-expen­sive, non-coat­ed papers and is suit­able for long print­ing runs with­out the plates wear­ing out.

Litho colour print­ing, which can be in line or halftone, requires a sep­a­rate plate for each colour. Mul­ti­colour press­es are fre­quent­ly used. One mod­el, called the Web Off­set machine, prints four colours in quick suc­ces­sion and on both sides at once of a con­tin­u­ous web of paper fed from reels.

Photogravure

PhotogravurePrint­ing by pho­togravure is exact­ly the reverse of print­ing by let­ter­press. Instead of the ink being applied to raised type or dots, it is con­tained in tiny hol­lows or cells, recessed below the sur­face of a cop­per-plat­ed, steel cylin­der.

The type mat­ter and illus­tra­tions are pho­tographed, and trans­par­ent pos­i­tives are made. These are laid down in their cor­rect posi­tions on a glass screen. The assem­bled pos­i­tives are then trans­ferred pho­to­graph­i­cal­ly onto a paper coat­ed with a light sen­si­tive gela­tine and known as a car­bon tis­sue. The car­bon tis­sue has already been exposed to light through a screen made up of a cross hatch of fine, trans­par­ent lines which form a pat­tern of tiny, light proof squares. The light has the effect of hard­en­ing the gela­tine in the cross line for­ma­tion whilst leav­ing the square dots unaf­fect­ed. When the pos­i­tives are pho­to­graph­i­cal­ly exposed to this pre­pared sur­face the light begins to hard­en the dot areas too, but this hard­en­ing process varies accord­ing to the light­ness or dark­ness of the details on the pos­i­tives.

The car­bon tis­sue is placed around a cop­per-plat­ed cylin­der and the back­ing paper is removed with water. The water also has the effect of dis­solv­ing away the gela­tine, but the light-hard­ened areas tend to resist this and the result­ing gela­tine lay­er there­fore varies in thick­ness.

Final­ly, the cylin­der is etched in a bath of acid. The thin­ner parts of the gela­tine etch away before the thick­er parts and, even­tu­al­ly, the cylin­der has cells of vary­ing depths; the dark­er the tones the deep­er the cells.

When it is quite cer­tain that no alter­ations or cor­rec­tions have to be made, the sur­face is giv­en a hard chromi­um fac­ing in order to make it hard wear­ing.

Photogravure Printing

Photogravure printingAll gravure print­ing machines work on the rotat­ing prin­ci­ple, as with litho, but no water is used and there is no process of off­set­ting onto a rub­ber blan­ket. The print­ing area of the cylin­der comes into direct con­tact with the paper. Machines can be of the web-fed vari­ety in which the paper is run con­tin­u­ous­ly from reels, or sheet-fed in which the paper is cut into sheets before print­ing.

The low­er por­tion of the etched cylin­der is con­stant­ly immersed in a reser­voir of ink which flows thick­ly over the whole cylin­der as it rotates. The cylin­der also runs in con­tact with a thin steel blade known as a doc­tor blade. When the ink-cov­ered area emerges from the reser­voir the sur­face is scraped clean by the blade, leav­ing only the ink held in the cells which prints on the paper in the famil­iar dot for­ma­tion.

You can always dis­tin­guish gravure print­ing from the oth­er two main process­es by exam­in­ing the type­mat­ter under a mag­ni­fy­ing glass. You will find that all the let­ters, as well as the illus­tra­tions, are repro­duced by dots because the type and illus­tra­tions are pho­tographed togeth­er through the same screen. It will be seen, also, that the dots in gravure print­ing vary in den­si­ty as well as size.

Mul­ti-colour gravure machines are com­mon. A sep­a­rate cylin­der is used for each colour and the paper is passed between rollers from one to the oth­er.

Screen Printing

Screen printingScreen print­ing, which has devel­oped rapid­ly over recent years, and there are now sev­er­al very advanced machines for doing it.

The sys­tem uses a screen made of a sub­stance such as silk, nylon or fine wire mesh fit­ted with­in a frame. A sten­cil of the let­ter­ing or design to be print­ed is firm­ly attached to the under­side of the screen, which is then fit­ted down onto the mate­r­i­al that is to take the impres­sion. It may be paper, glass, met­al, plas­tic, fab­ricâ-” almost any­thing. Ink is then forced through the screen by means of a squeegee and the inked image of the sten­cil is trans­ferred to the mate­r­i­al. The ink cov­er­age by this process is so good that light-coloured inks can be print­ed on dark back­grounds; even white on black.

Screen print­ing is nev­er employed for the nor­mal range of print­ed mat­ter. It is com­par­a­tive­ly slow com­pared with the oth­er process­es, and although it can now be used for half-tone and colour work the result tends to appear coarse. It is ide­al for bold dis­plays, for print­ing direct­ly on awk­ward shapes like bot­tles or plas­tic con­tain­ers, and it is exten­sive­ly used for print­ed elec­tri­cal cir­cuits.

Finishing, paper and ink

How a book is made — Making Up and Finishing

FoldingWhen the print­ing oper­a­tion is com­plete, the sheets are held in stacks. They have been print­ed on both sides with the var­i­ous areas of type and illus­tra­tions imposed so that when the sheets are fold­ed they form the pages of the mag­a­zine, book or what­ev­er it is. The in­dividual oper­a­tions dif­fer accord­ing to the size and kind of book con­cerned and the type of machin­ery used.

The stacked print­ed sheets are tak­en from the machine room to the ware­house from where they can lat­er be drawn in con­ve­nient quan­ti­ties and trans­ferred to the bindery. In the bindery they are cut into sec­tions suit­able for fold­ing. The fold­ing is done by machine. The machine shown uses both the knife fold­ing and the buck­le fold­ing devices illus­trat­ed in the dia­grams. In each case the paper is pushed between two revolv­ing steel rollers which com­plete the fold. The paper moves on through the machine and the action is repeat­ed until the right num­ber of folds have been made in each direc­tion.

After fold­ing, a pile of sec­tions is put into a bundling machine which com­press­es them, gets rid of the air from between the pages and makes them into a com­pact bun­dle. Next, sec­tions are placed in their cor­rect order in a gath­er­ing machine which col­lects them togeth­er in sets, each set of sec­tions now rep­re­sent­ing one book.

BindingThe sec­tions are then sewn. This is done by open­ing each sec­tion in the mid­dle and plac­ing it on the sad­dle of a sewing machine. The sad­dle swings round and locates the sec­tion under a row of thread­ed nee­dles, which stitch togeth­er the lay­ers of paper in the fold. The machine works auto­mat­i­cal­ly, deal­ing with the sec­tions rapid­ly — one after the oth­er. The sets of sec­tions mak­ing up each book then go for back-strip­ping where a strip of linen is glued down the sewn edges to hold them togeth­er. Final­ly, a three-knife trim­mer is used to first cut the top and bot­tom edges of the book and then the front. This trims the paper to the right size and cuts off the out­side folds so that the indi­vid­ual pages can be opened.

While the inside pages are being dealt with, the cov­er has been made in a case-mak­ing machine. The two parts are glued togeth­er in a cas­ing-in machine and, after press­ing, the book is com­plete.

Paper and Ink

PapermakingPaper is large­ly made from wood-pulp, although espar­to grass from Spain and North Africa is some­times used for par­tic­u­lar­ly good qual­i­ty papers. Wet pulp is con­tained in a tank at one end of a paper-mak­ing machine. It enters the machine and flows over a vibrat­ing wire-mesh con­vey­or which allows most of the water to drain through. The remain­ing fibres cling loose­ly to one anoth­er and are then passed between rollers which com­press them togeth­er. After final dry­ing between heat­ed rollers, the paper is wound onto large reels. Dif­fer­ent kinds of paper vary in the amount and kind of pulp used and in the pres­sures applied dur­ing rolling. Some kinds are coat­ed with a chi­na clay or plas­tic solu­tion to give them a fine, smooth print­ing sur­face.

Print­ing inks are not like the inks we use for writ­ing but are of a greasy, paint-like sub­stance which adheres to the paper as a thin film with­out blot­ting or run­ning. They can be of any colour for print­ing sep­a­rate­ly, one at a time, but for the four-colour print­ing process the pri­ma­ry colours of yel­low, red and blue are spe­cial­ly pre­pared to a stan­dard colour spec­i­fi­ca­tion. This enables them to be print­ed one with the oth­er, and it is the com­bined effect of these spe­cial tones, plus black, that gives a coloured print its nat­ur­al appear­ance.