Painting by Immersion and by Compressed Air: A Practical Handbook

One of the most difficult tasks of the finishing room foreman is to be certain that the proper reduction is made for the first and other undercoats. This is entirely eliminated with the use of the Standard system of piano finishing. This process alone makes it possible to apply a minimum quantity of varnish sufficient to withstand the strain of rubbing and polishing. This lessens the possibility of shrinking and cracking which excessive varnish coats applied by brush involves. The slower the speed of the lift, the less varnish is applied to the work, consequently there is a gradual regulation of the amount of varnish for the separate coats.

The foregoing description, together with the accompanying illustrations, will enable the reader to understand the general method adopted. It should be added that it is applicable to many other articles besides piano cases.

The system described was invented and is controlled by the Standard Varnish Company of London and New York.

Wheels.

An extremely ingenious but effective machine for coating hickory wheels with paint or japan is in use at the works of the Ford Motor Company, Trafford Park, Manchester. It consists of a stationary cylindrical vessel of exactly the right size to receive a wheel, which, being placed in position, is at once lowered into a tank containing the japan. Here it is made to revolve very rapidly, by which means the japan is thoroughly distributed over every part. Hickory, being a hard and comparatively non-absorbent wood, the japan might give too thick a coating if dipped and left to dry in the ordinary way. To prevent this, the wheel, while still revolving very rapidly, is mechanically lifted out of the japan, and is held just above it, where it continues to spin. This has the effect of throwing off the superfluous japan by centrifugal force. The cylindrical sides of the apparatus catch the japan, and it runs down into the tank below. The wheels are then taken out by a man, who wears gloves, are stacked on edge in rows to dry, and, after an hour or so, they receive a second coat. After twenty-four hours, or less, they are ready for use.

The advantage of rapidly revolving the wheels is that anything in the nature of a drip is entirely eliminated. This machine can deal with 300 wheels an hour, so rapid is the process. At the present time the Ford Works are using 2,000 wheels a week.

Some Typical Plants.

In gathering information of up-to-date character to include in this book the author has visited various parts of the country, and through the courtesy of the firms mentioned below has examined the plants used successfully for the treatment of many different goods. The following is a brief description of some of the plants inspected, although it by no means exhausts the list:—

Carriage Department, Woolwich Arsenal.

The plant for painting wagons, etc., has been in use for about 12 years and has been eminently successful, it being found by experience that a paint applied by dipping proves equally durable to that formerly applied by means of brushes. Indeed, the durability is increased for the reason, which has been pointed out elsewhere, that the paint finds it way into open joints and crevices which could not be reached by a brush. In some cases a wagon is dipped bodily, while in others it is dismantled and the different parts are dipped separately; again, the smaller portions are placed in an open wire basket which is plunged into the paint. The building in which this painting is done is of considerable extent and a large paint tank is located at each end. A wagon on being completed, or in the case of an old wagon, after having been prepared, is brought to the first tank and is raised from the ground and lowered into the paint, where it remains for about half a minute. It is then immediately raised, allowed to drain over a tank for a few minutes, and then over an inclined floor for a further period. At the end of about half an hour a workman inspects the wagon or other article and removes any tears or runs which may have occurred. The paint being specially prepared this is not usually an arduous undertaking.

The illustrations show very clearly a coach body in process of dipping. Overhead rails run throughout the length of the building and upon these are suspended the painted wagons, which are gradually moved along with a very little exertion, such rails being slightly inclined to facilitate this. By the time the series of wagons reach the further end of the building they are ready to receive a second coat of paint, by being dipped in the second tank. This being done they are then moved back, being at once suspended on the rails until quite dry, when they are hoisted to the upper part of the building, where they are left suspended until they are required for use. The paint is, of course, a special one which is supplied in paste form having the necessary binding ingredients. The colour used is khaki, which is very durable, being composed of earth colours. The thinning is done on the premises and white spirit is employed for the purpose, not turpentine, which would be far too expensive. Formerly benzine was employed, but this necessitated the use of a fan to take away the fumes which came from the spirit. Such a fan is not now found to be necessary.

The tanks are fitted with iron covers bearing upon thick felt and are operated by means of levers placed at a distance, so that should a fire occur they can be closed at a moment's notice. The hoist is worked from the ground by electricity. Formerly the operator of the hoist was located in a cab near the roof, but it was felt that this would be a dangerous position in case of fire, and he now, as stated, does the work from the ground. The work done at Woolwich gives an excellent example of the actual saving which may be effected by using the paint dipping process. Before the painting plant was put in no fewer than 200 painters were constantly employed; now about 40 are fully able to turn out the same or even a larger number of wagons in a given time.

James Gibbons.

Most of the metal sheets as well as finished metal work of various kinds made at these extensive works at Wolverhampton are finished by dipping into special enamels or japans made by Messrs. Mander Bros. The dipping is done by hand and the pieces are placed at the side of the tank to drain. In some cases it is found necessary to go over the work slightly with a brush to remove tears, but such work takes only a few minutes and is used mostly as a precautionary measure.

One coat is usually found sufficient, and at the proper time the iron sheet or metal article is stoved at 250° F. to 300° F. for two hours. Many other articles are also dipped successfully.

Harrison, McGregor & Co.

In the extensive factories of this firm at Leigh, Lancashire, dipping by immersion has been successfully carried on for some years past. Various agricultural implements are dipped bodily in a tank of paint which is fitted with a worm agitator, and is of simple construction. The iron parts are dipped separately, being supported on suitable hangers, while the very small parts are placed in wire baskets for immersion.

Phillips and Son.

The paint dipping plant at these works, which are situated at Sherbourne Street, Birmingham, has been in successful operation for some years past and is applied principally to bedsteads.

The tank holding black japan measures about 5 feet by 18 inches and is some 9 feet deep. The bedstead head and foot are separately dipped by hand into the tank which contains black japan, and are immediately hung on a hook attached to a slowly travelling chain. This chain runs around a rectangular space, and beneath is a metal lined dripping floor. The stove is located diagonally from the tank, so that by the time the bedstead parts reach it the dripping has ceased and they are ready to be baked. The stoving is done at 320° F., and is continued all night. One coat is found to be ample.

A very ingenious arrangement is in use for the application of coloured enamels. Three shallow tanks are mounted on rollers running in angle irons one above the other in such a manner that any one tank may be pulled out when required for use free from the others.

As a rule three coats are given for white work and two for green, blue and most other colours. No white lead is used, but only non-poisonous colours. The stoving is done mostly overnight at a temperature of 250° F. A little rubbing down between coats is done with very fine glass or emery paper. The japans are made by Messrs. Thornley & Knight.

In these works safes are painted, but the work is all done by hand.

The Ford Motor Company.

The extensive works of this company, at Trafford Park, Manchester, contain as complete a plant for painting, japanning, enamelling and varnishing, as it has been the pleasure of the author to inspect.

With characteristic thoroughness every detail which will ensure a first class finish with a minimum of time and labour has been thought out and applied. The result is that not only is every part dealt with most expeditiously but one coat of paint is applied to the whole outer surface of a motor body in the almost incredibly short time of two minutes. Further details will be found in this book under the heads of "Flowing-on," "Motor Parts," and "Iron Rods."

Marshall, Sons & Co., Ltd.

This well-known firm of agricultural implement manufacturers have a large dipping plant at their Gainsborough works, which they employ for painting various agricultural machines made principally of red wood. Some idea of the extent to which this process is applied may be obtained when it is said that on an average nearly 5,000 pieces pass through the dipping plant every month. The process is particularly well adapted for threshing machines and for appliances of the kind which consist of thousands of holes bored in the wood. If the painting were done by hand it would take many hours to paint such a machine, while by dipping it is done even more effectually in a few minutes. The priming coat only is dipped after knots, etc., have been treated with shellac. The tank measures 21ft. long by 7ft. deep and 2ft. 3in. in width. An agitating apparatus is used and the lifting is done by pneumatic appliances.

Hayward Brothers and Eckstein, Limited.

The paint dipping plant in use at the works of this firm, at Union Street, Borough, S.E., is of a comparatively simple type, and consists of a shallow tank in which various cast iron and steel goods are dipped in horizontal position. As a rule, one coat of paint is given, but in certain cases two are required. The bottom of the tank is slanted, and the contents are stirred up from time to time, but no agitating apparatus is used. The principal goods painted by dipping are the frames of Hayward's lights, which are of cast iron and are dipped on one side only, the other side, after the glass is fitted, being done by hand. Metal casements are also dipped in considerable numbers, as well as treads and rises of circular staircases, straight staircases, balconies, etc. These, being made of ornamental open ironwork, contain a large number of small shaped holes, and the dipping process is found to be by far the most effective.

Another speciality of this firm are Hayward's patent steel collapsible gates. The first coat of paint is applied by dipping; this paint, being black, dries flat, i.e., without gloss.

The Crittall Manufacturing Co., Ltd.

These works are at Braintree, Essex, where a large amount of structural steelwork is produced, the chief manufactures being metal windows of all kinds, from the well-known steel casement and sash to metal windows for use in industrial dwellings and specially designed windows for various climates, steel fireproof doors, skylights, steel office and works partitions, shop fronts; frictionless ball race runners for sliding doors, etc.

Perhaps the most noticeable feature of these works as far as our subject is concerned, is the very complete system of overhead rails, by means of which the various metal goods produced in the different finishing shops are conveyed to one or other of the paint tanks and then, having been left to dry, are taken to store rooms ready for instant shipment. These rails facilitate handling of the various goods, and reduce the actual expenditure under this particular item to a minimum. The rails are L-shaped, the hanger used for each article or series of articles being of a simple character, consisting of two wheels bearing on the top of the upright flange, while rods secured by bolts pass through the horizontal flange and hold it in position.

We will first describe the tank used for dipping metal windows. This is 15ft. long by 12ft. deep and only 1ft. 6in. wide. Attached to the tank is a large dripping floor measuring some 15ft. by 21ft. covered with sheet iron and inclined toward the tank, so that the paint which drips on to it finds its way back into the tank through a grating provided for the purpose to take off any dried particles. The paint used in this work is made by Messrs. Docker Brothers, and weighs 13 lbs. to the gallon; one coat is found sufficient for the purpose. The sashes or casements being brought in from the finishing room on the overhead rail, they are lowered into the tank by means of a special lowering apparatus designed on the premises. Some idea of this may be had from Fig. 31. In order to keep the load steady during the time it is being dipped, a slight depression or dip in the rail is made immediately over the tank. The sashes are only left in the paint for a few seconds, and are then raised, allowed to drip over the tank for perhaps a minute or two, and then allowed to drip over the adjacent floor for perhaps a quarter of an hour or less. They are then taken farther along and the paint dries in about three hours. Sometimes two, four, six, or even eight casements may be dipped at the same time. Attached to the elevating and lowering apparatus are hooks which pass through one corner of the casements. This causes the parts to hang at an angle which facilitates running off of the paint.

We come now to the department in which the baking or stoving enamel is used as applied to metal furniture in general, as mentioned. In this case the articles are dipped in a manner very similar to that already described, excepting that a large hook, similar in shape to that shown in Fig. 32, is used to support the article to be dipped; the wide opening goes inside the box or file and holds it at an angle so that when it is lowered into the paint all parts are covered inside and out. A few minutes are allowed for dripping, and after two or three hours the articles are ready to be stoved. In this case, Messrs. Docker Brothers' standard colour, a very pleasing dark green, is used. The stoving takes three hours at a temperature of 240° F., or higher in some cases. The tank mentioned is, of course, considerably wider than that used for casements. The dripping floor is in this case inclined toward the centre, which in turn is inclined toward the grating just outside the tank itself. If necessary, special thinners are added to bring up the gloss, but, as a rule, this is unnecessary. It is desirable after the article is dipped to go over it once with a small brush to remove any drips or runs which may possibly appear.

Another very important point to be attended to is to exclude all dust, and for this purpose the Crittall Manufacturing Co. have erected in this department screens of wire of the finest mesh over windows, so that no air can pass into the room without the dust being screened off.

Excluding Dust.

A matter of very great importance, yet one which is frequently overlooked in painting iron and other goods which are to have a glossy finish, either air dried or stoved, is to exclude dust from the apartment in which the work is done. In many engineering shops the nature of the business gives rise to a considerable amount of dust, and if this is allowed to enter the paint shop it will be fatal to the appearance of the painted work, as many specks will inevitably settle on the work and mar its appearance.

A paint shop is best provided with a concrete floor, and this should be frequently cleaned. The workmen should wear clean overalls, frequently renewed, and even so small a matter as keeping the hair, beard, etc., clean and free from dandruff should be attended to. The doors are best if double, and thick felt may be used with advantage in the joints so as to practically seal the opening when the doors are closed. Air which is admitted, either through ventilators or windows, should be strained before entering the building, and for this purpose silk gauze of the finest mesh is usually employed. In some cases, cotton wool in addition is placed in such a position that the air must pass through it before entering the room. If these precautions are taken it will be found that the quality of the work is greatly enhanced.

It may be observed in this connection that it is important also to provide means of adequate ventilation of the apartment. Moisture charged air has a bad effect upon paint work. Extreme heat is unnecessary, but it is very important that the temperature be maintained at a uniform rate, say 60° F. If the room in which the painting is done is very hot, the paint will be affected and be likely to become too thin for its purpose; while, on the other hand, if the room or articles to be painted are very cold, the paint or enamel will have a tendency to congeal. Both of these defects can be remedied, as already stated, by a good system of ventilation and maintaining the heat, night and day, at a uniform temperature.

A Model Drying Room.

The immense importance of providing a uniform temperature and ensuring an adequate system of ventilation in the room in which goods are placed for air drying can hardly be exaggerated. Unless such a system is in use the actual drying may be greatly retarded and the work stand a chance of being spoiled.

In connection with some of the plant inspected by the author it must be admitted that the provision made in this respect falls far short of what is needed. In one case the work of rubbing down was proceeding in the same shop, although in a different part, in which various goods which had been dipped were hanging up to dry. It need hardly be said that under such conditions it was impossible to keep the work free from specks.

In other cases the drying rooms were inadequate because of the inefficiency of doors and windows. These, it may be remarked,should always be double so as to maintain the heat uniformly.

Every varnish user knows that a draught of cold air which is allowed to reach a coat of varnish while drying is fatal alike to its appearance and durability. The result is almost certain to be a case of "blooming," which to the uninitiated may be described as a film not unlike the bloom of a freshly coloured plum which comes on the surface of varnish exposed under such conditions. Those unacquainted with varnish vagaries are apt to regard this trouble as being the result of inferior materials used in its manufacture. As a matter of fact it indicates nothing of the kind because, speaking generally, the higher grades of varnishes are the most susceptible.

Without doubt the best and by far the most economical plan to adopt is to have a drying room specially built for the purpose of receiving the articles to be dried. If constructed on scientific principles this will not only give a uniform temperature entirely free from draughts and dust but will considerably expedite the work, thereby allowing of a quicker delivery of goods and effecting a great saving of valuable floor space.

The author inspected such a drying room at the works of Messrs. Pinchin, Johnson, and Co., Ltd., at Silvertown, and a description of it will doubtless prove of interest. It is built of 5-ply wood and is about 16 feet square, sufficiently large to hold two full-sized motor bodies or several dozen perambulators, hand wagons, etc. The actual size may, of course, be varied according to the size of and number of articles to be dried. Air is admitted through two ducts situated close to the floor through fine wire gauze, which is provided with a lifting cover by which the amount of air admitted may be regulated.

Immediately over the two air ducts mentioned is a coil of steam pipes which heats the air to, say, 110° F. This, of course, causes it to rise toward the ceiling, but the angle between the ceiling and wall is rounded off by a cove, so that the current of heated air is directed along the ceiling toward the centre of the room where there is another cove and beneath it a coil of cold air pipes which lowers the temperature somewhat. Thus is created a constant motion of the air which may be regarded as the essence of the system.

But there is another very important provision in the shape of an automatic control. This cuts off the steam when any desired heat is attained so that when the drying room is filled up at night before the works close it can safely be left until the morning when the drop in temperature will not be more than 2 degrees. The steam may be admitted at, say, 10 lbs. pressure, but as soon as the room is heated from 2 to 2½ lbs. will be found to be sufficient. The actual time for heating the room to 120° F. is from 15 to 20 minutes.

The speed with which work is turned out by this well-considered adjunct may be gauged from the fact that a panel may receive one coat of enamel and two coats of flatting varnish in one day, or four coats of japan in the same period.

In addition to the advantages mentioned is the most important one that the drying room renders the manufacturer who is fortunate enough to possess one quite independent of the weather. In the words of the inventors and patentees, "one enabled by its use to create one's own climate."

CHAPTER IV.

It will be observed that the earth colours, such as ochre, sienna, umber, etc., are all light pigments, and as they are also recognised as being the most durable, they are eminently well suited for use in many positions, although the colour is not always very agreeable. Precipitated barytes (s. g. 4.144) can be used up to, say, a proportion of 10 per cent.—not more; red lead (s.g. 8.681) cannot be used for this purpose, as it is far too heavy, and the same applies to English vermilion (s. g. 7.726). If, however, a bright colour is required, it may be obtained by dipping in Venetian red or Indian red and giving a second coat of crimson lake (s. g. 1.898), but a coat of varnish should be sprayed upon this for protective purposes.

In considering this subject, it is well to remember that much will depend upon the thickness of the vehicle used, as, clearly, a fairly heavy pigment will settle out in a thin vehicle much quicker than it would in a comparatively thick one. The successful paint, therefore, is one in which both considerations are taken into account.

Very rarely indeed does it pay manufacturers to attempt to grind or prepare paints themselves, and much greater satisfaction will be obtained by getting supplies from a reputable firm who have made a special study of the subject.

Sometimes a white paint is required for dipping, and in that case 30 lbs. of sublimed white lead, 10 lbs. of zinc oxide and 6 lbs. of gilders' whiting, with 4 lbs. of asbestine pulp, mixed with 9 lbs. of raw linseed oil, will be found to give good results.

A paint which dries with a gloss is often desired for the finish of many articles, and can be readily obtained by first priming, then giving a finishing coat of paint on it which has been mixed with sufficient varnish to produce the desired gloss. In some cases three coats may be given, namely, the first or priming coat, the second, which should be flat, or semi-flat, and the third a coat of varnish paint, which will dry with a gloss. It should be pointed out, however, that the finish obtained by these means is not a little inferior to that which may be produced by using over the priming one or more coats of flat paint of the desired colour and finishing with a coat of suitable varnish, which may be applied either by dipping or spraying, according to circumstances. A point here worthy of mention is one which every house painter is or should be well acquainted with, and that is that the coats of paint that are superimposed should be alternatively flat, i.e., without gloss, and glossy, in order that each may adhere closely to the other. If the article to be painted is wood or any other material which is of an absorbent character, a comparatively large amount of turpentine and oil must be mixed with it in order to allow for suction. This will dry with a semi-flat finish, and a glossy coat or one having more oil in its composition, may be applied over it. If a further coat is required it should be flat or nearly so, and in that case a finishing coat of varnish will probably be required. The paints for these purposes may be purchased ready made or ready for thinning down, from firms who have made a special study of the requirements.

The question sometimes arises as to whether paint dipping or spraying can be used advantageously when in the finish two or more colours are to be used. As a rule the difficulties can be overcome by dipping first or even the second coat, spraying on the third or finishing coat, using specially prepared masks or shields over those parts which are not to be painted with the particular colour in use.

The following useful information is taken from "White Paints and Painting Materials," by W. G. Scott, who was for sixteen years connected as paint expert with the Milwaukee Harvester Company and the J. I. Case Threshing Machinery Co. Mr. Scott therefore speaks from a wide experience. He says:—

A certain amount of oil must be present in dipping paints to act as a binder, and it is advisable to add a small quantity of varnish to hold the paint together. The desired features in a good dipping paint are: freedom of flow and proper drip; sufficient binder to prevent chalkiness and produce a firm coat; covering capacity and an even distribution of the paint.

Non-absorbent surfaces like metal and hard wood require less oil than the absorbent soft woods.

In the former case there is little or no penetration of the liquid portion of the paint, but with pine, bass wood, white wood, poplar, etc., nearly all of the liquid is absorbed or taken up by the wood, consequently with benzine only as a thinner there will not be sufficient binder present to hold the pigment when the thinner evaporates.

Whereas 5 lbs. of paste pigment or colour ground in oil and thinned with a gallon of benzine would produce a suitable primer on iron or other non-absorbent material, it would not answer for soft wood.

Dipping paints, as a rule, contain from 4 to 10 lbs. of paste per gallon of thinner, the primer containing less paste than the second coat paints.

The composition of the paste colour has much to do with the dipping paint; for instance, 5 lbs. of paste white lead to the gallon of thinner will cover and work better than a mixture consisting of half white lead and the other half made up of transparent pigments like china clay, barytes, etc., nevertheless a small amount of inert material is generally understood to be an improvement in the way of durability.

Asbestine, whiting, silica and china clay are the inert materials most often used in paste goods for dipping purposes.

Asbestine probably helps to hold the pigments in suspension better than any of the others and answers nicely for dipping paints, but, as previously mentioned, does not allow the paint to level out when used with a brush.

China clay, on account of its low specific gravity, is much favoured as a suspension agent, but materially lessens the opacity of the paint.

A small amount of whiting is a good addition to a dipping paint, as it carries down much of the dirt and heavy particles usually produced during the process of dipping. Silica gives the paint "tooth," and by some authorities is considered an actual necessity in primers which are intended to be sand-papered.

White lead and zinc oxide are the two ideal white pigments considered from a dipping standpoint, and it will be found that the majority of dipping paste paints on the market contain a notable quantity of zinc oxide, either straight or in the form of zinc lead.

Zinc oxide is generally the predominating pigment in the white and tinted paste paints, and is usually associated with white lead (basic carbonate), zinc lead, and sublimed white lead, mixed with more or less inert material according to the ideas of the manufacturer or in order to cheapen the product.

The admixture of inert material with the coloured pigments requires some knowledge of the composition of the coloured pigment; for instance, lampblack might be safely mixed with asbestine, whiting, silica, barytes, etc., without detriment, but yellow ochre containing, naturally, considerable clay and silica would hardly permit of any great addition of china clay or silica.

The strong iron oxides, chrome greens and similar tinting colours will stand a large quantity of inert material when the paint is to be used as a body colour, but for varnish colours it is customary to use the chemically pure colours and less paste per gallon of thinner.

Paste paint for varnish colours is frequently ground in oil, in japan, or in a mixture of the two, but far better results are obtained by grinding the dry pigment in varnish thinned to a grinding consistency with a little turpentine. A varnish with a viscosity of 20 (water = 1) which gives a stiff mix with, say, 5 lbs. of pigment will, when thinned to a viscosity of that of raw oil, i.e., a viscosity of 4, take about 20 lbs. of pigment.

No set rule can be given for the kind and amount of thinners to be used in dipping paints for various purposes, but the following proportions[1] will furnish a key to the general mixtures used:—

Primers for Metal.

4 to 5 lbs. of paste thinned with 7/8 to 31/32 gallon of benzine or turpentine and 1/8 to 1/32 gallon of mixing varnish.

Primers for Hard Wood.

4 to 5 lbs. of paste thinned with 15/16 gallon benzine or turpentine, 3/64 gallon raw oil, 1/64 gallon mixing varnish.

Primers for Soft Wood.

4 to 7 lbs. paste thinned with ½ to ¾ gallon benzine or turpentine, 15/32 to 15/64 gallon raw oil, 1/32 to 1/64 gallon varnish.

In some cases, with very soft, porous woods, it may be necessary to add more raw oil and some japan or liquid drier, but too much drier must not be added, as it will shorten the "flow."

Second Coat Dipping Paints.

5 to 10 lbs. of paste thinned entirely with benzine or turpentine, or with 7/8 gallon of solvent and variable proportions of oil and varnish according to the surface desired.

Varnish is advocated in all of these mixtures, as it helps to hold the solids and liquids together and prevent separation; it also induces toughness.

It is essential that a varnish be used which will mix perfectly with oil and benzine at a temperature of 60° F.

Varnish colours are best thinned with turpentine, but owing to the high price of turpentine the large factories insist on using benzine or some of the turpentine substitutes now on the market.

The fact that some of the turpentine substitutes work better and give a better "flow" with the paint and varnish, is due to the fact that most of them contain a heavy distillate of petroleum similar to kerosene.

Kerosene oil has the double property of thinning and imparting "flow" to either paint or varnish, but retards the drying, hence too much must not be used.

Damar varnish, which will not stand thinning with benzine without separation of the gum or becoming cloudy, will permit of dilution with kerosene to quite an extent.

So far as durability is concerned, kerosene imparts more durability and is more waterproof than any of the other thinners. Combined with rosin and manganese oxide, it may be made to dry like raw linseed oil, but, of course, does not possess the same properties.

In dipping paints, as in all other kinds of paints, good judgment must be used in the mixing, and it is absolutely essential that paints for soft wood, or other absorbent material, contain enough oil, or binder, to hold the pigment.

White Paste Primer. Extra Fine.

• 300 lbs. white lead (carbonate).
• 150  "  zinc oxide.
• 50    "  floated silica.
• Grind in 10 gal. raw linseed oil.
• Product = 575 lbs.

This paste is thinned with turpentine or benzine for dipping purposes in the following manner:—

White Dip for Metal.

• 100 lbs. of white paste.
• 14 gal. turpentine or benzine.
• ½  "  pale mixing varnish.
• ¼  "  white liquid drier.

White Dip for Hard Wood.

• 100 lbs. white paste.
• 13 gal. turpentine or benzine.
• 2     "  raw linseed oil.
• 1/4  "  pale mixing varnish.
• 1/2  "  white liquid drier.

White Dip for Soft Wood.

• 100 lbs. white paste.
• 12 gal. turpentine or benzine.
• 6     "  raw linseed oil.
• ¾  "  white liquid drier.

The pale mixing varnish and the white liquid drier must not liver with lead or zinc, otherwise, the paint in the tank will thicken continually.

The above formula produces one of the best paints known, and it is certainly not a cheap paint.

White Spirit.

As already mentioned, many firms who use the paint dipping process buy their paint in paste form with the requisite amount of driers added, and thin it themselves with white spirit, which is a petroleum product specially prepared for the purpose. Turpentine is, of course, too expensive, and the spirit costs, under normal conditions, little more than one-third of the price, although exact figures cannot be given owing to the fluctuation in the price of these materials. Some manufacturers use a white spirit, to which has been added from 25 to 30 per cent. of genuine American turpentine. This, of course, renders the mixture somewhat expensive, and possesses no advantage excepting that it gives the characteristic smell of turpentine; but this, it appears, is not important in a factory, and the pure white spirit is quite suitable in itself.

According to Mr. S. Roy Illingworth, A.R.C.Sc., A.I.C., B.Sc., Lond., expert to the Gas Lighting and Improvement Co., Ltd., turpentine substitutes were first placed on the market about 30 years ago, and consisted at that time of a mixture of turpentine and kerosene oil. Investigations led to the production of white spirit, drying as quickly as turpentine, or even quicker if desired. Several grades of this material are made, varying in flash-point from 80° up to 150°. The flash-point of genuine turpentine, it may be mentioned in passing, is 90° to 91°, and the 90° flash-point spirit is the one usually employed for painting purposes, although the 80° flash-point would answer equally well for dipping. The best grade is practically free from smell and is suitable for admixture in all paints, excepting those having a bitumastic or asphaltic base, or paints in which very common driers containing cheap rosin are used. A rough-and-ready test as to the quality of white spirit is to dip a piece of blotting-paper into it and hang it up to dry. In the course of an hour-and-a-half it should have wholly disappeared, leaving no smell or stain behind it. If there should be a stain the sample should be viewed with suspicion. Another test of the same kind is to drop a little spirit on a piece of white writing paper and to leave it for three-quarters of an hour, when it should have disappeared without leaving a stain. In addition to these tests it might be advisable to mix a little spirit with paint and to try it experimentally.

In the evaporation of turpentine it is usually admitted that a small proportion, say, from ·25 to ·50, is left behind owing to oxidation. In the case of best white spirit, however, very little residue will be left behind, certainly not sufficient quantity to interfere in any way with the drying. The use of the spirit has proved so successful that practically nothing else is now employed in paint dipping. It is, however, important, of course, that the best quality white spirit be used, but as this is so much less in cost than turpentine, there is no temptation to use an inferior quality.

The Quantity of Paint Required for Dipping and Spraying.

Speaking generally, rather less paint will be required when it is applied by dipping, or spraying, than is necessary when it is applied with a brush. But there are many exceptions, particularly in spraying, where it may be necessary to give a coat considerably thicker than usual.

The following table will be found useful as a guide, but it should be remembered that the actual space covered will vary considerably with different grades of paint, so that the table should only be taken as approximately correct. In cases of doubt, careful calculations should be made after a given quantity of paint, varnish, or lacquer has been applied to a surface of known area. This will serve as a useful guide in ordering in the future. It need hardly be said that the quantity of paint necessary will vary largely with the surface to which the paint is applied. For example, an absorbent surface, such as unprimed wood, will require much more paint than metal work, which absorbs little or none.

Spreading Capacity of Paints.