The art of lithography : a complete practical manual of planographic pringting

Preface

Ten years ago the lithographic trade was in a critical position, and it was an open question whether it would improve or go under. Thanks, however, to a number of remarkable inventions, in processes, in machinery, and in the purely chemical aspects of the art, a great revival was brought about, with the result that lithography is better able to hold its own in the printing world to-day than at any period in its past history. The most pressing need of the trade at the present time is an ample supply of workmen of all-round competence, and it is with the object of helping to meet this need that the author has undertaken the preparation of this manual.

The work is the result of long experience both in the workshop and the technical classroom, and the author has sought to make it comprehensive, thoroughly up-todate, and, above all, practical. Every lithographic operation is described in the fullest detail, and useful practical hints will be found on almost every page. It completely meets the requirements of the lithographic syllabus of the City and Guilds of London Institute in all grades.

Certain processes of great importance and value are described in the book for the first time, particularly the simpler and cheaper transferring method dealt with in Chapter XI and the practical aerograph process set forth in Chapter V. The important question of the training of apprentices is also fully dealt with. Special attention is directed to the very full combined index and glossary.

The author gratefully acknowledges the invaluable assistance of many firms and individuals, especially in

Vlll PREFACE.

those chapters that treat of subjects not within his own immediate knowledge and experience. Mr. Walter Murray has supervised the work throughout from an editorial standpoint and has read all the proofs, besides preparing the index. Special mention should also be made of Messrs. James Brown & Co., Esk Paper Mills, Penicuik: Messrs. Morris & Bolton, Ltd., London; and Messrs. Furnival & Co., Ltd., Eeddish. Hurst's treatise on " The Theory of Colour" (Scott, Greenwood & Son), Sindall's "Paper Technology " (Charles Griffin & Co., Ltd.), and Hind's " A Short History of Engraving and Etching " (Archibald Constable & Co., Ltd.) have been of th^ greatest service.

H. J. E.

January, 1914.

CHAPTER I. The Basis of Lithography

Planography — A Chemical Process — Some Chemical Terms — Action of Oleic and Arabic Acids — An Outline of the Lithographic Process.

CHAPTER II. Lithographic Stones

The Solnhofen Quarries— The Origin of the Solnhofen Stone — The Archseopteryx — Qualities of Stones — Backing Thin Stones — Preparation of Stones — Importance of Uniform Thickness- Testing Stones — Stone-polishing by Chemical Means — Grain ing Stones — The " Hansa" Automatic Stone-grinding Machine — Thickness and Weight of Standard Sizes of Stones.

CHAPTER III. Aluminium and Zinc Plates 17

Occurrence and Properties of Aluminium — Graining of Aluminium Plates — Plate-graining Machine — Finishing Operations — Removal of Work from Plates — Occurrence and Properties of Zinc — Preparation of Zinc for Lithography — Graining Metal Plates by Hand — The Relative Values of the Different Printing Surfaces.

CHAPTER IV. Chemicals and other Materials Used in Lithography ... 22

Chemical notation.

List op Planographic Materials — Acetic Acid — Alum — Ammonium Nitrate — Ammonium Phosphate — Asphalt — Beeswax — Benzoline — Bichromate of Potash — Carbolic Acid — Castor Oil — Caustic Potash — Caustic Soda — Chromic Acid — Citric Acid — Crayons — Cuttle-fish Bone — Dabbers and Daubers — Damping Cloths — Dextrine— Flake White— French Chalk — Gelatine — Glass Powder — Glycerine — Gold Size — Gum Arabic — Gum Asphaltum — Gum Elemi — Gum Gamboge — Hydrochloric Acid — Indiarubber — Lampblack — Lavender Oil — Linseed Oil — Litharge — Magnesia — Naphtha — Nitric Acid — Offset Powder

CONTENTS.

PAGE

— Oleic Acid — Oxalic Acid — Palm Oil — Paraffin Oil — Paraffin Wax — Peasemeal — Phosphoric Acid — Pitch — Plaster of Paris — Potash, Caustic— Pumice Stone— Resin — Rubber — Sand — Shellac — Soap — Soda, Caustic — Sodium Phosphate — Sponges — Starch — Stearine — Suet — Syrup — Tallow — Tarn o' Shanter Stone — Terebene — Turps — Varnish (Litho) — Vaseline — Water of Ayr Stone — Whitening.

Chapter V

Methods of Lithographic Drawing — Number of Printings — The Work of the Prover — Making a Key — Guide Lines and Register Marks — Offsets or Faints — Reversing the Key — Offsets or Faints for Offset Machine Work — Hand Stippling — Shading Mediums — Finishing Stipple Work — Crayon Work — Treating Crayon Work on Stone — Treating Crayon WTork on Metal Piates — Aerograph or Air-brush Work (The New Lithography)— The Air-brush — The Process — Preparing the Stone for the Work — Gumming-out or Stopping -out — Preparing the Stone for Proving, Printing, or for Transfers — Splash Work — Photo-chromolithography — Proving Chromo-lithographic Work — How to Ensure Perfect Register — Prevention of Offsetting.

Hand-press Printing — Business Cards, Invoices, etc. — India Paper Prints.

CHAPTER VI. Transfer Papers and Inks 49

Kinds of Transfers — Varieties of Transfer Papers — Stone-to-stone and Stone-to-plate Transfer Papers— Scottish Transfer Paper — Berlin Transfer Paper — French Transfer Paper — Semi-moist and Ever-damp Transfer Papers — Copperplate Transfer Paper -Letterpress-to-stone (or Metal Plate) Transfer Paper — Photo-litho Transfer Paper — Litho-writing Transfer Paper — Grained Transfer Paper — Materials for Coating Transfer Papers — Recipes for Transfer Paper Coatings— Materials Used in Making Transfer Inks — Recipes for Transfer Inks.

Chapter VII

Transfer Impressions — Copperplate Press and Accessories— Copper and Steel Plate Transfers — Testing for Pressure — Inking over and Pulling the Transfer — Quality of Paper — Offsetting Copperplate Transfers — Effect of Unequal Damping — A Quicker Process for Copper and Steel Plate Transfers — Advantages of Stone Engraving — Decline of Stone Engraving in Britain — American Commercial Stone Work— Preparing a Stone for Engraving on— Inking-in the Engraving— Pulling the Transfer — Photo-litho Transfers.

CONTENTS. • XI

Chapter VIII. Page

Patching or Imposition of the Transfers 66

Introductory — Gripper Allowance — TestiDg the La3T-out Sheet — Imposition of the Pages — The Margins — Sticking down the Transfers— The Key Sheet — Treatment of Small Patches.

CHAPTER IX. Hand and Power Transferring and Printing Presses . . 73

Mechanism of the Transferring Press — The Broadway Press — The Top-lever Press— Tympans — Scrapers — Need of Uniform Pressure— Adapting the Scraper to the Scraper-box — Bed of the Press and Packing — Cleanliness Essential.

Chapter X

A Fascinating Art — Importance of Cleanliness — General Considerations in Transferring — The Transferring Process in Outline — Treatment of Stones with Alum Solution — Effect of Alum Treatment — Warm Stones — Other Methods of Preparing a Stone — Testing the Scraper — Adjusting the Pressure — Transferring the Work to the Printing Stone — Preparing the Stone for Desensitizing — Acid Resists — The Inking-in Process — A Better Method of Inking-in— The First Etch— The Second Etch— Defects of the Above Method — The Great Principle of Transferring— Rubbing and Rolling- up — Summary.

A Detailed Practical Description — The First Inking — Applying the Acid Resist — Picker and Polishing Stone — The First Etch — Preparation for the Second Etch — The Second Etch — Etching for High Relief — Transferring Autographs to Stone — Transferring to Metal Plates — Zinc Transfers — Aluminium Transfers — Cleaning-up Metal Plates.

CHAPTER XI. A Simple, Labour-saving Transferring Process .... 94

Established Practice — Great Care and Skill Required — The Troubles Obviated by a New Process — The Arobene Treatment Described — The Two Methods Compared — Advantages of Arobene — Treatment at End of Day — Preparation for Machine — Arobene for Proofs.

CHAPTER XII. Reducing and Enlarging by Machine Process .... 97

Usefulness of Reducing and Enlarging Machines — The Fougeadoire Machine — Coating for Rubber ^heet— Application to New Work — Proper Condition of Coating — Taking the Impression — Burnishing— The Reducing or Enlarging Process — Application to Chromo Work.

Xll CONTEND 8.

Chapter XIII. Page

Transposing and Revebsing 102

Meaning of Transposition — The Relief or Polishing Method — The Gum Method— The Transfer Method — Principle of the Transfer Method — Reversing Transfers — The "Reverso" Transfer Reversing and Offset Proving Press — The "Reverso" for Proving Offset Work — Other Uses of the " Reverso ".

Chapter XIV

Paper-making Materials— Rags— Esparto — Wood Pulp — Other Materials— The Process of Paper-making — Preparation of the Raw Material — Making of the Pulp or Half-stuff — Bleaching the Pulp— Beating the Pulp — Loading, Sizing, and Colouring — Hand-made Papers — Machine-made Paper — Finishing Operations— Art Papers — Mixing of Pulps — Physical Qualities of Paper — Paper and Moisture — Lithographic Requirements in Paper — Standard Sizes of Writing and Printing Papers — Standard Sizes of Cards.

CHAPTER XV. The Theory of Colour - . . . . 125

Light and Colour — The Nature of White Light — The Spectrum of White Light — Coloured Bodies — Luminosity of Colours — Primary and Derived Colours — The Mixture of Coloured Lights — Complementary Colours — The True Primary Colours — Contrast of Colours — Colour Harmonies.

Chapter XVI

Constituents of Printing Inks — Linseed Oil — Boiling the Oil — Black Pigments — White Pigments — Blue Pigments — Red Pigments— Yellow Pigments — Green Pigments — Brown Pigments — Purple, Violet, and Mauve Pigments— Permanence of Pigments— Transparency of Pigments — Tints, Mediums, and Pomades — Drying of Inks — The Mixing of Inks — Varnishable and Non-varnishable Inks — Preparation of Inks by the Lithographer— Consistency of Inks — Driers in Chromo Work — Printing Tints.

Chapter XVII

Lithographic Printing Machines. Direct Flat-Bed Machines. 147

Introductory — Types of Lithographic Printing Machines — The Direct Printing Flat-Bed Machine — The Frame — The Carriage — The Impression Cylinder — Driving the Carriage — Driving the Cylinder — The Cylinder-starting Arrangement — A Double Inking Mechanism — The Cylinder-locking Arrangement — Tbe Furnival Cylinder Brake — Other Cylinder Brakes — Air-eushioning Cylinders — The Inking Mechanism — The Damping Mechanism or Water Motion — Tbe Feeding Mechanism — Tbe Delivery Mechanism— The Machine Brake.

CONTENTS. Xlll

Chapter XVIII. Page

Machine and Hand-press Rollers 163

The Different Kinds of Rollers — The Forme-inking Rollers — Nap Forme-inking Rollers — Glazed Forme-inking Rollers — Rubber-covered Forme-inking Rollers — The Ink-distributing Rollers — The Rider Rollers— The Vibrating Ink Ductor Roller— The Forme-damping Rollers — The Vibrating Damping Ductor Roller — The Water-fountain Roller — Hand Rollers.

CHAPTER XIX. Introductory

The Direct Rotary Machine— The Frame — The Plate Cylinder — The Impression Cylinder — The Inking Mechanism — The Damping Mechanism — Feeding and Delivery Mechanism — The Slow Turning Motion.

The Flat-bed Offset Machine — Introductory — The Transfer or Offset Cylinder — The Impression Cylinder — Feeding and Delivery Mechanism — Prevention of Doubling — Conversion to Direct Machine.

The Rotary Offset Machine — General — The Transfer or Offset Cylinder — The Impression Cylinder — The Feeding Mechanism — The Delivery Mechanism — Device for Ensuring Register — Gear Marks — Power for Lithographic Machines.

Automatic Accessories of Lithographic Machines — Automatic Feeders — The Harris Feeder — The " Slogger " Feeder — The " Dexter " Feeder — The Jogger — The Automatic Counter.

Chapter XX

Introductory — The " Wogdon " Improved Litho Press — Furnival & Co.'s Improved " Express" Direct Flat-bed Machine — The Scott Stop-cylinder Flat-bed Machine.

Furnival & Co.'s Flat-bed Offset Machine Attachment— The " Reliable " Flat-bed Offset Machine.

The " Reliable " Direct Rotary Machine— The L. & M. Direct Printing Rotary Machine — Furnival & Co.'s Direct Printing Rotary Machine — The Scott Direct Rotary Machine — R. Hoe & Co.'s Direct Rotary Press.

The "Baby" Rotary Offset Machine— The Waite Rotary Offset Machine— The L. & M. Rotary Offset Machine— The Furnival Rotary Offset Press — The Harris Automatic Rotary Offset Press — The Scott Six-roller Offset Press, with "Dexter" Feeder.

George Mann & Co.'s Two-colour and Perfecting Rotary Offset Machine — R. Hoe & Co.'s Two-colour Rotary Press — R. Hoe & Co.'s New-pattern Two-colour Rotary Press — R. Hoe & Co.'s Three-colour Rotary Press.

XIV CONTENTS.

Chapter XXI. Page

Machine Management 21S

Method, Order, Cleanliness — Requirements of the Machineman — Acquaintance with the Machine — Attention to the Cylinder — The Cylinder Brush and Grit-guard — The Cylinder and Flywheel Brakes — The Flyer Drum — The Gearing — The Stone or Bedplate Carriage — The Under-parts — The Side Rails — The Air-cushioning Cylinders — The Ink Duct — The Water Duct or Fountain— The Damping Slab — The Machine Belts — The Cylinder Coverings.

CHAPTER XXII. Machine Printing from Stone 225

Setting the Stone — Mixing the Ink — Ink for Bright Enamel Papers — Washing-out the Work — Taking the Impression — A Register-finder — Three Great Principles in Printing — Overlaying the Cylinders — Gaining Experience — Doctoring Thickened Work — Doctoring Weakened Work — Paper-creasing at the Machine.

CHAPTER XXIII. Printing Chromo or Colour Work 234

Interesting but Anxious Work — Precautions against Bad Register — The Keystone — Bronze and Metal Leaf — The Safety Vacuum Bronzing Machine — Hints on Bronzing — The Rotation of the Colours — Print the Outline Forme Early — Double Printing and Double Rolling — The Cause of Setting-off — Prevention of Setting-off — Register — Some Causes of Inaccurate Register — Improvement of Register — Unequal Damp and Pressure — How to Remedy Expansion of the Paper — Altering a Section.

CHAPTER XXIV. Machine Printing from Metal Plates 24G

Flat-bed Printing — The Iron Bedplate Supports — Printing from Metal Plates — Effect of Gum on Metal Plates — An Experiment.

Rotary Printing — The Principles — Setting the Pressure — Register on Rotary Machines — The Automatic Damping Apparatus — The Forme-inking Rollers — Special Precautions on Offset Machines — Cylinders True with each other — The Rubber Blanket — Inks for Offset Machines.

CHAPTER XXV. Special Finishing and Other Processes 252

Varnishing Lithographed Work — Gelatining Lithographed Work — Finishing Chromo Work — Roughing Printed Work — Graining Printed Work — Embossing — Spangle and Kindred Work — Graduated Tint Printing— Rainbow Printing — Printing Trans parencies.

CONTENTS. XV

Chapter XXVI. Pack

Direct Photo-lithography in Line and Half-tone . . . 258

Direct Photo-lithography — The Line Process — The Half-tone Process— Half-tone Lithography — Ordinary Three-colour Work.

CHAPTEE XXVII.

Litho Printing on Fabrics and Tinplate : Decalcomanie Transfers 261

The Older Process for Silk and Calico— The New Method— The Older Process of Tinplate Printing — Direct Tinplate Printing — Decalcomanie Transfer Printing.

The Relation of Estimating to Costing — A Sample Estimate and Cost Sheet — The Elements in Price — Cost of Production — Two Forms of Oncost — Departmental Oncost — Office Oncost.

CHAPTER XXXI. The Training of Apprentices 287

Explanation — An Expensive Luxury — Responsibility of Employers — An Apprentice Guardian Committee — The Term of Apprenticeship— Suitability of Lads — An All-round Training Necessary — A Suggested Course — Technical Education.

Combined Index and Glossary 295

Chapter I. The Basis Of Lithography

Planography. — The art of printing from a polished calcareous stone was invented by Aloys Senefelder, a native of Prague, Bohemia, about the year 1796. The name Lithography (from the Greek words, lithos, a stone, and grapho, I write) was given to the process, and this is still in general use, although to-day it by no means adequately represents the art as it did up till about a quarter of a century ago, because of the extensive and ever-increasing employment of zinc and the introduction of aluminium as printing surfaces. Accordingly, the word might with advantage be replaced by another which will convey a broader meaning. The term Planography (from the Latin word, planus, level, flat, plane) has been much in evidence of late, and there is no reason why it should not be generally adopted to denote all processes of printing from flat surfaces.

A Chemical Process. — Lithography (or planography), being a flat-surface process, occupies an intermediate position between letterpress or relief printing and copperplate or intaglio (sunk) printing ; but with this essential difference, that while letterpress and copperplate printing are mechanical processes, planography is of necessity a chemical one.

If a printer's inking roller is passed over a letterpress forme, the raised face of the type, which represents the actual work, is immediately charged with ink, whilst no ink is deposited on the supporting base of the plate. But if the roller is passed over a plane, level surface, such as a lithographic stone or a marble slab, which has not undergone any previous preparation, it will deposit ink over the entire surface. Therefore, in planographic printing two forces or materials are necessary : one that will attract printing ink to the parts where it is required, that is, to the work which is to be printed, and another that will repel it from all other parts ; and this can only be brought about by the aid of chemistry. The separation between the printing and the non-printing surface, which is effected in letterpress printing by means

V THE BASIS OF LITHOGRAPHY.

of the mechanical device of relief, is effected in lithographic printing by the action of suitable chemicals.

Some Chemical Terms. — Before proceeding to explain the chemical actions employed in lithography, it is necessary to define some chemical terms for the guidance of non-chemical readers.

Chemically all substances are classed as elements and compounds. An element is a simple substance, such as sulphur or oxygen, that cannot be resolved into any other substance. A compound is a chemical combination of two or more elements. For example, sulphuric acid consists of hydrogen, sulphur, and oxygen combined in certain definite proportions. A compound of an element with oxygen (one of the gases in the atmosphere) is called an oxide of the element. Thus water is an oxide of hydrogen. So compounds with sulphur are called sulphides ; compounds with chlorine, chlorides ; and so on. Compounds of elements with hydrogen and oxygen are called hydrates. Thus caustic soda is the hydrate of a metal called sodium.

A large class of chemical compounds called salts are produced by the combination of a base with an acid. A base is usually the oxide or hydrate of an element : for example, ferric oxide, which is an oxide of iron occurring in many iron ores, and caustic soda. An acid is a compound of hydrogen, usually with a sour taste, that has the property of turning a vegetable blue, such as litmus, to a bright red. When a base combines with an acid, the element intthe base displaces the hydrogen in the acid, and forms a salt. Thus, when caustic soda combines with hydrochloric acid (a chloride of hydrogen), the sodium in the caustic soda takes the place of the hydrogen in the acid, and sodium chloride (or common salt) is formed. So also, when lime, that is, oxide of calcium, combines with sulphuric acid, a salt called sulphate of calcium is formed.

Certain bases, such as caustic soda, reverse the reddening action of acids on vegetable blues, and restore the blue colour. These are called alkalis. Substances which are neither acid nor alkaline in their action on litmus are said to be neutral.

For lithographic purposes a distinction between fatty or oily acids and water acids is useful. The former are fats and oils, such as stearine (or stearic acid) and oleine (or oleic acid), possessing a sour, rancid taste and an acid reaction. The latter are acids either soluble in water or intimately miscible with it. Examples of these are the familiar substances, nitric acid, sulphuric acid, and citric acid.

Action of Oleic and Arabic Acids. — Acids play the most important part in the chemistry of lithography, inasmuch as they combine with the bast1 or element in the printing surface

OUTLINE OF THE LITHOGRAPHIC PROCESS. 6

to form other compounds which are absolutely necessary for the successful working of the process. Certain fatty or oily acids form the ink-attracting and water-repelling compound ; and certain water acids form the ink-repelling and water-attracting compound. If a drop of oleic acid (or oleine) is put on a prepared lithographic stone (which mainly consists of limestone, that is, carbonate of calcium), or on a zinc or aluminium plate, an oleate of calcium, zinc, or aluminium is almost immediately formed ; then, if the remaining portions of the surface are treated with a suitable water acid (arabic acid, contained in gum arabic solution), an arabinate of calcium, zinc, or aluminium is formed. If the stone or plate is then dampened with clean water, and the inking roller passed over it, it will be found that the roller deposits ink only on the oleates (the parts which have been acted upon by the oleic acid), and that the remaining portions, so long as they are kept damp, repel the ink. This, then, is the fundamental principle upon which planography is based.

An Outline of the Lithographic Process. — Before proceeding further, it will be helpful to give here a general outline of the process of lithography. This will enable the reader to understand in some measure technical terms that have to be introduced in advance of their full explanation. The original " copy " for the lithographic artist may be a drawing or a sketch, a photograph or a model. The work must be first drawn upon lithographic stone, or upon a zinc or aluminium plate, or upon a specially prepared paper called transfer paper. Special soapy inks and crayons are used by the artist for drawing the original work.

A proof is a completed print taken from the original drawings on the stone or the metal plate, and a transfer is an impression or print pulled on transfer paper from an original drawing, or from a letterpress forme, or from an engraving done on stone or on copper or steel plate. These transfers are all pulled in special greasy inks called transfer inks. A transfer may also be written or drawn with soapy inks and crayons on transfer paper. The transfers are patched or fixed in position on a sheet of the paper to be printed on, and afterwards transferred to a printing stone or metal plate.

The stone or plate is then placed in the printing machine. There are several kinds of printing machines. In those known as flat-bed machines the printing surface travels backwards and forwards in the bed of the machine ; but in others, called rotary machines, the printing surface (which in this case must be a metal one) is bent round a cylinder. Some machines print direct from the printing surface on to the paper, whereas in

4 THE BASIS OF LITHOGRAPHY.

others the work on the stone or plate prints on to a rubber blanket on a cylinder, and this in turn transfers the impression to the paper. The former are called direct printing machines, and the latter offset printing machines. Where a job is in several colours, each colour involves a separate printing forme and a different ink.

Chapter II. Lithographic Stones

The Solnhofen Quarries. — Lithographic stone is composed almost entirely (about 97 per cent) of carbonate of lime, otherwise called carbonate of calcium. It is a stratified rock, that is, one that has been deposited in layers, and the world's supply comes chiefly from a small district in Central Bavaria, where

Fig. 1. — Map of Central Europe, showing position of Solnhofen.

there are a number of quarries (Fig. 2). The centre of this district is a place called Solnhofen (Fig. 1), some sixty miles north-west of Munich, and about ten miles north of the River Danube, from which river-bed the sand is obtained for the purpose of grinding the face of the stones before they leave the quarries. The texture of the stone is very compact and homogeneous ; it is hard, a a

OKIGIN OF THE SOLNHOFEN STONE.

RECENT PERIOD the presen M&n Appeared on The

PLEISTOCENE OR GLACIAL PERIOD .

Boulder clay e lc

PLfOCEINE SYSTEM

OLIGOCENE SYSTEM

EOCENE SYSTEM

CRETACEOUS SYSTEM London Clevy ere yet easily fractured ; and it varies in colour from blue-grey to pale buff. It is easily worked and cut into sizes to suit the requirements of the printer.

The Origin of the Solnhofen Stone. — It may be of interest to the young lithographer to have some idea as to how this rock, which has proved to be of such great value to the world, came to be there. The geological age in which it was deposited is that called by geologists the Jurassic, from the Jura Mountains, on the frontiers of France and Switzerland. The Jurassic Age is much more recent than the Coal Measures, but it ended long before the advent of man on the earth. Fig. 3 gives a rough idea of the geological position of the Solnhofen limestone.

The regions in which German lithographic stone is now found were, perhaps millions of years ago, covered with large lakes or seas, or the estuaries of rivers which flowed into the seas. These rivers would, after continued heavy rains, become much swollen, and carry down to the lakes or seas great quantities of stones, sand, mud, minerals, etc., which would be deposited by gravity in regular order. If we take a large clearglass bottle and fill it three parts full of water, and stir into this one or two handfuls of earth, we shall find upon allowing all to remain undisturbed for some time that the water has again

become quite clear, and the earth which we mixed with it has been deposited in layers. The sand and grit went quickly to the bottom ; the less heavy particles gradually fell on top of the sand ; and so on, until there was nothing left in the water but the very finest and lightest sediment, which slowly settled down on top of all.

JURASSIC SYSTEM

-Solnhofen Lithographic UmesTone Bird (Arcbrcop>eijx^

Th« olde<

TRIASSIC 5YSTEM •

OR NEW RED 5AND5TOME The earliest Mammals

PERMIAN SYSTEM

The ea.rlife:5,r f^e p I 1 1 e ^,

CARBONIFEROUS SYSTEM The GreAl Co.n1 Depo^.L,

DEVONIAN

jWjn^y I vrt n i,

Old red samostomk

ORDOVICIAM

The e

3ILURIAM SY3T£M

ifcst Fishes

CAMBRIAN

Slates

SYSTEM

OLDEST BRI (

*ock OtHObirS

N.W. SCOTLAND)

Fig. 3. — Kelative Geological Position of the Solnhofen Lithographic Limestone.

Now, if we go down, after several days of heavy rain, to the mouth of a small river or stream, where it runs into the sea, its course far out into the ocean may easily be followed with the eye, because of the brown, muddy line it has made for itself through the clear water. The same thing is happening here as took place in the bottle, but this time it is in a current instead of in still, confined water ; and we may easily imagine that, once out of the great force and dash of the stream, the coarse and heavy particles in the form of small pebbles will soon settle at the bottom, and a little beyond, where the current is less strong, the sand will gather. But the water is still heavy and thick with fine insoluble matter. This, too, although it may be miles farther out, will all gradually settle.

It is estimated that, on an average, every 100.000 lb. of river water contains 21 lb. of mineral matter, of which 11 lb. is carbonate of lime ; the balance being made up of carbonate of magnesium (a constituent of litho stone), sulphate of magnesium, common salt, silica, etc. When we consider that the amount of mineral matter in solution carried annually to the sea by such a river as the Thames is estimated at 548,230 tons, we are able to form some idea how sedimentary stone, such as we use for lithographic printing, was gradually built up. This gradual building up may go on for thousands or even millions of years, the weight and pressure increasing as time goes on, causing the under layers to become very firm and hard ; until at length a gradual upheaval of these parts takes place, and the deposits are exposed as dry land.

The Archaeopteryx. — Many interesting fossils, representing both land and water life, are found in lithographic stone. Of these the most interesting by far is the Archceopteryx (see in Fig. 4), of which there are only two specimens in existence, one in the British Museum in London, and the other in the Royal Mineralogical Museum in Berlin. The Archceoptery.r is the earliest known bird, and still retains many reptilian characters, so establishing the evolution of birds from reptiles. It was about the size of a rook.

Qualities of Stones. — Besides Bavaria, lithographic stone is found in Spain, France, Italy, America, and England (Somersetshire), but it is all of a more or less inferior quality, and need hardly be considered in connection with our subject. Even from the best quarries in Bavaria the quality varies considerably, both in texture and colour. The best stones are of a pale yellow colour and free from chalk marks or veins, but there is also a light grey variety, which is harder than the yellow stone, and is in great demand by American lithographers, as work is inclined to print sharper from it. This suits their tine commercial en-

LITHOG-BAPHIC ■ FOSSILS.

Archcsopteryx. .(Royal Mineralogical Museum, Berlin.)

Archceopteryx. (British Museum.)

A Fish (Leptolepis). A Crustacean (Mecochirus).

Fig. 4. — The Archaopteryx or Earliest Known Bird and other Fossils found

in Solnhofen Limestone.

gravings, which are so much admired in Britain. Both of these qualities are unfortunately getting very scarce and costly, hut nevertheless it pays the printer to buy only the best ; and this being so, the greatest possible care is exercised by the quarrymen when taking out large slabs. These slabs are rarely more than 5 or 6 inches in thickness, the superfluous stone from the thick ones being chipped away until the necessary thickness is obtained.

Backing Thin Stones. — A stone of otherwise good quality but too thin is sometimes cemented to another thin stone of inferior quality. This is done by first grinding the stones, one on top of the other, with sand and water until they are perfectly true with each other. The sand is then washed off and the surfaces dried or left wet according to the nature of the cement to be used. A quantity of the cement is put upon one of the newly ground surfaces, and the other stone is again placed on top. The top stone is then worked about until the cement has spread evenly but thinly all over both of the surfaces, so that the stone can only be moved with difficulty. They are then left in position with weights on top for a few days until the cement has hardened. A cement which is said to be useful for this purpose (Paget's Mastic) may be made as follows. Knead to a paste 21 parts chalk, 63 parts sand, 5 parts white lead, and 2 parts litharge, with a saturated solution of acetate of lead, and finally mix with 6 parts linseed oil. The surfaces should be dry when this cement is applied.