Gold Ink, Bronzing and Foil Printing

The use of gold, when com­bined with good design, gives to cer­tain kinds of print­ing a dis­tinc­tion and qual­ity unob­tain­able by any other means.

Gold print­ing is used in the pro­duc­tion of high-class labels, wrap­pers, box tops, cov­ers, greet­ing cards and other work where bright, showy effects are appro­pri­ate.  Gold and other metal­lic col­ours are pro­duced by the let­ter­press pro­cess in three dif­fer­ent ways –

  • Metal­lic Ink: print­ing dir­ect, using gold ink made from bronze powder, or sil­ver ink made from alu­minium powder or paste.
  • Bronz­ing: print­ing first with a tacky pre­par­a­tion and imme­di­ately dust­ing with bronze, alu­minium or other metal­lic powder which adheres to the tacky preparation.
  • Foil Print­ing: metal foils are pressed on the paper or other stock after the man­ner of block­ing. The foils are usu­ally sup­plied with an adhes­ive dress­ing which is made act­ive by heat, so that heat as well as pres­sure is required to attach it to the paper or stock. Foils other than metal are avail­able and the pro­cess is lim­ited to platen and block­ing presses

Gold Ink

The dif­fi­culties asso­ci­ated with print­ing gold ink by the let­ter­press pro­cess and the rel­at­ively poor res­ults obtained on any other than coated or glazed stocks must be admit­ted. The ink is made from very fine bronze powder sus­pen­ded in a spe­cial oil var­nish vehicle, and it is not a homo­gen­eous com­pound. Some ink firms sup­ply the powder and vehicle sep­ar­ately for mix­ing in small quant­it­ies fresh at the machine, with improved res­ults. On cover paper, bonds and other rough-finish papers, it is advis­able to use a neut­ral size base for the first impres­sion and print the gold on the base. This helps to lift the gold ink from the plates. A second work­ing in the gold ink is also prac­tised and gives a brighter effect, but this is likely to be marred by feathered edges around the designs.

For best res­ults, the rollers of the press must be in per­fect con­di­tion and set as only an expert can set them, with exact con­tact through­out. The impres­sion must be light and level; excess­ive pres­sure moves the soft ink to the edges of the design. Making-ready should be accom­plished with some thin, light-coloured ink, and the gold ink mixed and run up fresh when the job is per­fectly ready for the run. In mix­ing the gold ink it should be kept thin so that it runs off the palette knife-never short and buttery-and only a small quant­ity should be mixed at a time. When mak­ing two work­ings in the gold to get a brighter effect, the ink on the first work­ing should be kept sparse and the effect obtained on the second work­ing. Register must, of course, be per­fect. The machine must be washed up whenever the quick dry­ing ink begins to thicken on the rollers, or when the qual­ity of the work deteri­or­ates, which is usu­ally after a run of about two hours. It must also be washed up at the mid-day break.

The above remarks apply also to sil­ver ink, although this is not quite so dif­fi­cult to work and the res­ults obtained are bet­ter. The ink, sup­plied ready mixed, is made from alu­minium powder, and com­par­at­ively recent devel­op­ments in the meth­ods of man­u­fac­ture have greatly improved the product.

Fre­quently an addi­tional work­ing in gold or sil­ver is required in four-colour pro­cess work, and gen­er­ally speak­ing, with these light formes and good qual­ity coated papers, metal­lic inks are ideal for this pur­pose and have proved a great boon.

Bronz­ing

Kolbach Bronzing Machine

Kolbach Bronz­ing Machine

By far the greater bulk of let­ter­press work in gold is pro­duced by bronz­ing, and the res­ults obtained by this method are excel­lent. The pro­cess involves, first, print­ing the sheet in a tacky medium such as bronze pre­par­a­tion and then dust­ing it with bronze powder which adheres to the pre­par­a­tion. It is then lightly burn­ished to smooth and brighten the bronze and the loose bronze is cleaned off the sheet. Small work can be bronzed by hand, but the work must be car­ried out under vacuum. Bronz­ing machines have been avail­able for a period of years.

Home Office Reg­u­la­tions. All bronz­ing work is reg­u­lated by Home Office Reg­u­la­tions, a copy of which may be obtained from H.M. Sta­tion­ery Office.

The Bronze Pre­par­a­tion. A brown pig­ment con­tain­ing copal var­nish and gold size is used as pre­par­a­tion, and is sup­plied in dif­fer­ent grades by all ink man­u­fac­tur­ers. When the design is prin­ted and bronzed the pre­par­a­tion should dry hard on the sur­face of the paper by oxid­a­tion, and so hold and seal the bronze which is dus­ted on.

The dif­fi­culties asso­ci­ated with the pre­par­a­tion are: pluck­ing; fail­ure to hold the bronze (which may remain mod­er­ately loose on the paper and come off in hand­ling); dry­ing on the machine.

Pluck­ing. The nature of the pre­par­a­tion to hold and seal the bronze on the paper must be strong and tacky. Noth­ing of a pen­et­rat­ing nature such as raw lin­seed oil or greasy solid solvents should be added if it can be avoided. The best res­ults are obtained by work­ing it as stiff as pos­sible, so that it is on the verge of pluck­ing all the time. Two grades of pre­par­a­tion should also be stocked, one stronger than the other, so that either may be used alone or blen­ded to suit the require­ments of the par­tic­u­lar paper. Boiled lin­seed oil (which does not pen­et­rate) may be used spar­ingly as a redu­cer. The speed of the press should be reg­u­lated to suit the paper, and pro­duc­tion must be con­tinu­ous because the slight­est delay allows the pre­par­a­tion to begin set­ting on the machine and pluck­ing is inevitable.

Bronze not Hold­ing. This is one of the major prob­lems encountered in bronze work. If the bronze rubs off, the appear­ance of the work is marred, and with food con­tain­ers (chocol­ate wrap­pers, etc.) the slight­est trace of loose bronze can­not be tol­er­ated. To pre­vent this the work is often over­prin­ted with a very thin film of var­nish to seal the bronze.

The dif­fi­culty arises chiefly in con­nec­tion with absorb­ent papers which allow the pre­par­a­tion to pen­et­rate so that insuf­fi­cient remains on the sur­face to hold the bronze.

The pre­par­a­tion should have the right char­ac­ter­ist­ics so that it is largely a ques­tion of the quant­ity car­ried, which should allow for the pen­et­ra­tion that takes place and yet leave suf­fi­cient on the sur­face of the paper to hold the bronze.

This is not easy, as designs will often include extremes of solid and fine detail and the solid areas will require so much pre­par­a­tion that the fine detail will fill in.

The work often takes the form of large sheets prin­ted from elec­tro­types moun­ted on one large mount. Much can be done in the method and man­ner of the making-ready. The plates will need inter­lay­ing so that the solid parts are well up to type height, but the fine detail (as, for instance, long imprints in five-point lin­ing sans) is kept slightly below type height. The work on top (cyl­in­der) must also be care­fully car­ried out, and all fine detail must fin­ish quite level but light. In this way it will be found that much more pre­par­a­tion can be car­ried (without filling-in) to hold and seal the bronze.

When the actual bronz­ing is tak­ing place some dis­tance away from the print­ing press, the sheets have to be car­ried in batches and there is the risk of the pre­par­a­tion partly dry­ing before the sheets are bronzed, the hold­ing power of the pre­par­a­tion being largely lost. Notice should always be taken of the last sheet bronzed in each batch. This should be dus­ted clean occa­sion­ally to ensure that the pre­par­a­tion is not too dry to take the bronze. The num­ber of sheets car­ried in each batch can then be arranged accordingly.

Dry­ing on the Machine. Owing to its quick-drying nature the pre­par­a­tion should not be runup on the machine until the job is ready to run, making-ready being accom­plished with a non-drying ink. Dur­ing the run, the machine should not be allowed to stand, as even a stiort delay will allow the pre­par­a­tion to set. The machine will require wash­ing up at mid-day as well as at the end of the day’s run. As far as pos­sible no non-drying solvents should be used in bronze preparation.

The Bronze Powder. Gold bronze powder is made from cop­per, brass and zinc alloy. The mol­ten metal is reduced in the pro­cess of man­u­fac­ture to minute leaf particles and sifted through fine silk. It is then graded in degrees of fine­ness by grav­ity, greased and pol­ished, but its flake-like form is retained. In addi­tion to the stand­ard tones (pale, rich pale, and rich), deeper gold tones are pro­duced by the applic­a­tion of heat. There are also copper-coloured bronzes (made from cop­per), sil­ver (made from alu­minium), and other col­ours such as green, blue and fire-red, which are obtained by the use of dyes.

The finest tex­ture powders have the best cov­er­ing power, but are inclined to “pick up” on pre­vi­ous work­ings on the sheet and also stick to the paper-resisting dusting-if the paper is at all rough, as cover paper, etc..The coarser bronzes will, there­fore, be found more suit­able for such con­di­tions. If coarse bronze “picks up” on pre­vi­ous work­ings on the sheet, the fault lies with the pre­vi­ous work­ings which have not dried cor­rectly. Great care in the choice and treat­ment of the ink is neces­sary when there is to be a sub­sequent work­ing in bronze. How­ever, the trouble can be cured or min­im­ized by adul­ter­at­ing the bronze with mag­ne­sia powder, but in extreme cases the work will have to be treated with mag­ne­sia alone before the bronz­ing operation.

Hand Bronz­ing. Hand bronz­ing is used only for small sheets and com­par­at­ively short runs on platen presses. The work must be car­ried out under vacuum, and it is uneco­nom­ical to handle sheets lar­ger than crown by the hand pro­cess. Up to this size, with proper arrange­ments, noth­ing excels the hand pro­cess for quality.

A use­ful piece of equip­ment is the Vacuum Hand Bronzer (Mark Smith pat­ent), which com­prises a hand bronz­ing table of box-like con­struc­tion and a slop­ing glass front through which the worker can watch his work. At the back is a vacuum box with a suc­tion fan driven by a small built-in motor which also drives a dusting-off device. For dusting-off pur­poses the sheets are pushed one at a time between two rollers through a long slot in the vacuum box and with­drawn against the action of the rollers which revolve inwards together and clean both sides of the sheet. The loose bronze is sucked away by the fan which also draws away all loose bronze dur­ing the pro­cess of hand bronz­ing. (See Fig. 1.)

A large pad of cot­ton wool, enough to fill the hand is used for the bronz­ing. The bronze is first lightly dus­ted on, care being taken to avoid smear­ing the pre­par­a­tion, and then rubbed harder to burn­ish.; On rough-surfaced papers the bronze must not be rubbed so hard that it becomes ingrained into the, paper around the design; if this occurs, it will be very dif­fi­cult (if not impossible) to dust off. The pre­par­a­tion gradu­ally impreg­nates the sur­face of the cot­ton wool, which should be changed fre­quently by pulling the wool apart; and turn­ing it about, oth­er­wise the pad will mark the work.

The sheets should be car­ried to the hand bronzer in small quant­it­ies that can be dealt with before the pre­par­a­tion becomes too dry to pick up the bronze prop­erly. Con­stant atten­tion must be given to this.

When the bronzed work is dry, it can be cleaned of all loose bronze in the dust­ing rolls or oth­er­wise with cot­ton wool by hand under vacuum.

Machine Bronz­ing. When large quant­it­ies of bronze work are handled the work will be prin­ted in large sheets on cyl­in­der presses and run through bronz­ing machines. The sheets can be car­ried from the one machine to the other in dozens sup­por­ted on a card, placed on the flat feed-board of the bronz­ing machine, and hand fed. The speed of the two machines should be reg­u­lated so that there is no delay.

Two main types of bronz­ing machine are avail­able* the cyl­in­der type and the more mod­ern end­less flat belt type.

Mark Smith Vacuum Bronz­ing Machine, There is still a good deal to be said in favour of the old cyl­indrical style of bronz­ing machine which gives long and reli­able ser­vice. A large drum cyl­in­der with tum­bler grip­pers and a flap (which closes the gap in the cyl­in­der and so pro­tects the lead­ing edge of the sheet) takes the sheet from the front lays, which swing away. As the sheet moves for­ward, it passes under the duct in which a plush-covered roller revolves and flicks the bronze on to the sheet. Duct leads con­fine the bronze lat­er­ally to the lim­its of the design, and the turn of the duct roller is adjus­ted for length by a ratchet and pawl arrange­ment to con­fine the bronze to the depth of the design. Ranged around the cyl­in­der are the vari­ous dust­ing on, burn­ish­ing, and dust­ing off rollers and devices (thir­teen in all) covered with plush and mon­key skin. The two burn­ish­ing rollers are of dif­fer­ent dia­met­ers and revolve at dif­fer­ent speeds, and also have a lat­eral recip­roc­at­ing motion. The last two dusting-off rollers make con­tact with the deliv­ery drum and so clean the back of the sheet. The bear­ings of all rollers are held in slots for instant­an­eous adjust­ment: of contact.

The whole machine is effi­ciently boxed in, and there should be a win­dow for gen­eral inspec­tion pur­poses. Sur­plus bronze drops to the bot­tom of the machine where it is drawn up by means of a suc­tion fan and con­veyed by a wide pipe back into the duct. The action of the fan exhausts the air inside the machine and cre­ates a par­tial vacuum so that air is con­tinu­ally drawn into the machine from the room and takes any loose bronze with it. Over the duct the bronze drops down by grav­ity, and the con­duct­ing air escapes upwards along a pipe into the out­side atmo­sphere. The machine is simple to adjust and work, and every part is read­ily accessible.

Flat-bed Bronz­ing Machines. The latest type of bronz­ing machine is the flat-bed style. The sheets are led into the machines by an adjustable roller and are car­ried through on an end­less rub­ber blanket; there are neither lays nor grippers.

In some of the machines the bronze is dus­ted on by oscil­lat­ing pads (“Mil­wau­kee,” “Fur­ni­val” and “Omega”) and in oth­ers by end­less plush bands work­ing across the machines (“Laco”). Pads are also employed to burn­ish and smooth the bronze on the design. There are lat­eral dusting-off bands to remove the sur­plus bronze; these make con­tact with brushes and in this way keep clean them­selves. The final dust­ing off is done by rollers which clean the sheet just before deliv­ery. All the rollers, pads and bands are adjustable.

The machines are fully enclosed and are fit­ted with exhaust fans and air ducts. The strong internal vacuum draws all sur­plus bronze away, and it is auto­mat­ic­ally filtered and gathered to be used over again when freshened up with new bronze.

This type of machine is often described as “port­able” because it is moun­ted on castors and can be moved about the machine-room from one press to another. It is, how­ever, heavy and dif­fi­cult to move among the other machines.

As all the oper­a­tions of bronz­ing, burn­ish­ing and dust­ing are done on the flat, these machines are of greater length than bronz­ing. machines of the cyl­in­der type and take up con­sid­er­ably more floor space.

Coup­ling the Bronz­ing Machine to the Print­ing Press. Some­times the bronz­ing machine is coupled up to the print­ing press so that the sheets run dir­ect from one machine to the other. Where the amount of bronze work war­rants this, it is an excel­lent arrange­ment. Apart from the sav­ing in time, which is con­sid­er­able, there is no delay between the print­ing and bronz­ing and the prin­ted sheets are bronzed in the cor­rect sequence, with max­imum effi­ciency. Both styles of bronz­ing machine lend them­selves read­ily to the coup­ling sys­tem, the cyl­indrical style being coupled on and driven by the print­ing press through a con­nect­ing shaft and mov­able clutch. This neces­sit­ates a car­riage con­tain­ing trav­el­ling tapes driven from the bronz­ing machine end (which can be sup­plied or made to specification).

The two-revolution press deliv­ery is suit­able for this prin­ciple, the sheets passing from the tapes of the press to the tapes of the con­nect­ing car­riage and so to the bronz­ing machine, where a slop­ing tape feed is suf­fi­cient without other attach­ment. When not in use the car­riage is pushed up out of the way and held by counter weight. This arrange­ment allows the print­ing press to run on other than bronze work when required, and in the mean­time the bronz­ing machine may be used for dust­ing, etc.

In flat bronz­ing machines, the coup­ling arrange­ments are sim­pler and, as they have no grip­pers or lays, the need for exact tim­ing is not so neces­sary. The machines can be driven inde­pend­ently and the speeds synchronized.

Foil Print­ing

The use of foils in rolls has been developed in con­nec­tion with book­bind­ing for block­ing the titles and designs on the fronts and spines of cov­ers for books, etc. These foils are usu­ally made on rolls 200 ft. in length, on a back­ing of glassine paper, and can be sup­plied in any width. They are pre­pared with an adhes­ive sur­face ready for block­ing on almost any mater­ial, and the heat and pres­sure used in the press at the time of block­ing fixes the foil to the mater­ial. Foils are man­u­fac­tured in genu­ine gold (22 and 18 ct.), imit­a­tion gold, sil­ver, a-large range of metal­lic and flat col­ours and white. (V. Gould­ing and Co.
Ltd.)

The Machines. Vari­ous machines are avail­able for using foil, ran­ging from small hand machines to large power block­ers, incor­por­at­ing roll feed attach­ments for the foil, and giv­ing impres­sions up to 25 per minute. Brass dies, brass type, or spe­cial elec­tro­types and ste­reo­types are fixed to the upper platen (or bed) of the press, which is heated to 200F., and guides are fixed to the lower platen (or drawer) so that the cov­ers are set to a cent­ral pos­i­tion in line with the dies. Between the two platens is the foil, which runs off the roll in front of the machine and between two rollers at the rear so that a con­tinu­ous strip of roll leaf runs across the face of the die. Under pres­sure the heat fuses the adhes­ive so that the design in foil adheres to the stock and is pulled away from the back­ing paper. The scrap foil remains on the back­ing and is rewound at the back of the machine. At the same time a new sur­face of foil is pulled over the die ready for the next impres­sion. The roll feed attach­ment will draw any length of foil up to the full capa­city of the heater plate. Other types per­mit the draw­ing of two or more dif­fer­ent widths and lengths; this makes it pos­sible to cover dif­fer­ent sizes of impres­sion on the same die or dies, with min­imum waste of foil. Dif­fer­ent col­oured foils can be used simultaneously.

The advant­ages of foil print­ing for vari­ous oth­er­wise dif­fi­cult sur­faces and mater­i­als (as com­pared with the lift­ing and dry­ing of ordin­ary print­ing inks) are now real­ized, and the pro­cess and machines are used for print­ing on cel­lu­loid labels, radio pan­els and parts; metal and plastic name­plates, dials and sci­entific instru­ments, etc Dur­ing the war, foil print­ing was used widely for the speedy pro­duc­tion of instruc­tion labels, name­plates, etc., for air­craft, tanks and ships, each of which requires num­bers of labels, either in metal, plastic or trans­fer; of these, mil­lions were printed.

Foil Print­ing on Platen Presses. Roll feed attach­ments and heat­ing plates are also suc­cess­fully fit­ted to platen presses of both the dir­ect approach and clam-shell types, the attach­ment con­form­ing to the style of the par­tic­u­lar press, e.g. “Peer­less” roll feed attach­ment (see Fig. 2) is read­ily fit­ted to the heavy-duty “Crafts­man” or the “Vic­toria” presses. The heater plate is also sup­plied com­plete with rheo­stat con­trol, reg­u­la­tion switch and clips for hold­ing the plates; the fit­ting of these attach­ments to equip the machines for foil print­ing in no way inter­feres with the ink­ing mech­an­ism of the press for ordin­ary work.

Foil Print­ing and Emboss­ing. When platen presses are fit­ted with roll leaf feed attach­ments for foil print­ing, the prin­ciple also lends itself to the applic­a­tion of foils and emboss­ing in one oper­a­tion for the pro­duc­tion of high-class cov­ers, show­cards, greet­ing cards, box tops, etc. The work is very effect­ive and dis­tinct­ive on any kind of stock. With dark cover stocks the opaque flat col­oured foils are often an improve­ment on ordin­ary print­ing inks. The emboss­ing die is made ready in the usual way and forces made, and the con­tinu­ous strips of foil are run over the heated die so that the stock, foil and back­ing are all, embossed together, the foil being released from the back­ing to adhere to the stock. A fea­ture of the work is the’ per­fect register as the foil print­ing and emboss­ing are accom­plished in the same operation.

His­tor­ical art­icle from the Brit­ish Printer

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