Reproduction of Article "A Modern British Dye Factory", Chemistry & Industry, Vol. 44, No. 51, December 18, 1925, pp. 1218-1225:
Whatever the demerits of British manufactures they are generally accorded the tribute of soundness and durability, and in the production of fadeless textile materials this
country has also taken a considerable part. The modern period of guaranteed fabrics was only made possible by the discovery of the Indanthrene series, but although it has
taken nearly twenty-five years for the properties of these products to be adequately realised, they were made use of as early as 1903 in the Sundour fabrics, the first series of
guaranteed fadeless fabrics in this country. In fact the Sundour series played a substantial part in the establishment of the Indanthrene colours on the market and, by 1914,
“Morton Sundour Fabrics Ltd.” was probably the largest single consumer of these dyes.  The outbreak of the war threatened to put a stop to this development, and the
avoidance of this by the formation by Mr. James Morton of the concern which later became Scottish Dyes, shows clearly the position of the company in the British fast-colour
movement, a position which has been since consolidated by the company’s own contributions to this branch of chemistry. In 1914 these colours had not previously been
made outside Germany, and both the already existing and newly formed English manufacturers were then concentrating their efforts on the commoner and better-known
colours. It was these circumstances which prompted a textile concern, Morton’s Sundour Fabrics, Ltd., to try to manufacture its own colours, and the courage of this policy
cannot be discounted by the claim of necessity.  Between the designing, weaving and even dyeing of fabrics, and the making of dyestuffs, there can be but little connexion ;
but in November, 1914, Indanthrene Yellow G was produced in small lots, and by February of the next year in bulk. This was given the name of Caledon Yellow G, and it was
soon followed by other Caledon colours of similar type. In March, 1916, a second series was begun, and Alizarin Saphirol, the first member of the acid alizarin series, was
made as Solway Blue. By June, 1917, the progress which had been made with the Caledon and Solway series was so satisfactory that the dyemaking was made a separate
concern under the name of Solway Dyes, Ltd. The original works was, at this time, extended by the building of new chemical houses and a separate block of laboratories,
and further additions were made as demanded by increasing production, and about a year later the present company was formed. A little later, however, the possibilities of
the site at Carlisle were exhausted, and it was decided to build new works on a site offering adequate room for expansion. Building was begun at Grangemouth in 1919. In
the design of these works the experience gained at Carlisle was utilised, and both buildings and equipment were conceived on up-to-date lines. The works are admirably
situated n the industrial centre of Scotland, being midway between Glasgow and Edinburgh, and also for shipment home and abroad, as they are close to the Grangemouth
docks, to the Forth and Clyde Canal, and are connected with the L.M.S. and L.N.E.  railways.  Ample space for expansion is available.

The general layout is rectangular, the chemical houses being arranged in parallel rows, in the centre. The main laboratory has ground and first floors with wide central
corridors dividing each into two parallel series of separate laboratories.  These include the main analytical laboratory which traverses the whole width of the building at the
west end on the ground floor; two dye-testing laboratories, model dyehouse, balance room, sample room, store-rooms, library, offices and research laboratories.  The
equipment throughout is in accordance with modern university practice. The research laboratories are separate, self-contained units, each occupied by either one or two
chemists and their assistants. The roof is flat; a portion is occupied with exposure tests on dyed fabrics. The laboratories at Carlisle are on a similar plan, but are only about
half the size of those at Grangemouth.

Great attention is given to analysis and standardisation. Raw products are analysed on entry, intermediates at most stages of manufacture, and dyestuffs during the final
stages. During 1924, over 25,000 samples were analysed or tested for dyeing properties in the company’s laboratories. An important section of this work is the examination
and approval of finished batches of colour. The manufacture of the dyestuffs themselves is carried out in the chemical houses. Most of these houses (Fig. 2) are rectangular
buildings 160 ft. long by 60 ft. wide, well separated, so that alterations and additions may be made to them without interfering with each other or encroaching on the main
lines of communication. In addition to the chemical houses and the laboratory buildings, there are the general stores, the engineering workshops, the power plant and meter
houses. A complete service of gas, water, steam, vacuum and compressed air is supplied to each chemical house from the central stations. The high-pressure autoclaves
(Fig. 3) are housed in a special building ; they are deeply sunk into the earth with parapets built up to the level of the lids and lightly roofed over on a steel framework.  During
building, processes were started up in the various sections of the plant as they were completed, and the works are now running at full capacity, including many units not
contemplated in the original scheme.

In an account of Scottish Dyes, mention cannot be omitted of its loyal and enthusiastic staff, both chemical and commercial. Beginning from a very small nucleus, like the
firm itself, every member who has joined has stayed on and is with the company at the present time. The present body of between twenty and thirty chemists is entirely
British, and is drawn from practically every university in the Kingdom.  Probably the moat remarkable feature of all is that not one of the chemists had ever worked previously
in a dyestuff factory.

Turning to developments in products, it has already been mentioned that manufacture began first with the fastest vat series and then with the fastest wool series, and this
standard has been maintained.  Extension has only taken place by the introduction of new products of fastness corresponding to that of dyes already made. Up to 1923 the
Caledon and Solway colours were the only two series, but in that year the Celatenes were introduced and now occupy a position with regard to acetyl-cellulose silk corn
corresponding to those held by the Caledon colours towards cotton and the Solway towards wool. Early in the present year the first of a fourth series, the Solcdons, was put
on the market. These are an attempt at producing a universal series applicable to all fibres with the fastness of the vat colours. A general idea of the chemical nature of the
Caledon and Solway colours can be seen from the formulae of a few of them given below.:—

The Solway colours contain sulphonic-acid groups and dissolve in water, dyeing wool from a slightly acid bath. The Caedon colours are dissolved by reducing with sodium
hydrosulphite in an alkaline bath to compounds such as that shown for leuco Caledon Yellow 3G. The Solway colours are used principally for wool, but also to a smaller
extent for silk. The Caledon colours are mainly for cotton, but are used also on silk, linen and artificial silk.        

The constitution of the Celatene colours has not been disclosed, but they are stated to be a new class of anthraquinone dyes, specially synthesised for the dyeing of
cellulose acetate silks. They are quite distinct from the Solway and Caledon colours and have not previously been used for the dyeing of other fabrics. They are analogous to
the Duranol colours of the British Dyestuffs Corporation, the two series having been discovered independently, but the patent rights of the root principle upon which many of
them depend are owned by the Corporation. Their great merits are fastness and the simple way in which they are used. They are in fact direct dyestuffs. They do not
generally dissolve completely at the commencement of the dyeing operation, but have great affinity for the acetyl silk, and as the dissolved dyestuff is taken up by this, further
colour goes into solution.  These two classes of acetyl silk colours mark an advance for which this country’s dye industry may claim considerable credit.

The remaining series is the Soledon group, which represents the most interesting of Scottish Dyes’ developments. It has already been seen how the most permanent
dyestuffs come in the Caledon series and that because of the difficulty of dyeing their use is mainly for cotton. The Soledon series represent an attempt at making the
Caledon colours easily available for the other staple fibres and, briefly speaking, they are derivatives of the Caledon colours which are soluble in water and which after
having been absorbed in the dyeing or printing processes are by a development treatment with an oxidising agent (which is distinct from the oxidation in vat dyeing)
reconverted to Caledon colours. The adequate consideration of these colours opens up one of the most difficult aspects of colour chemistry. Three colours of this range
have up to the present been made available.

Apart from these new series some new colours have been added to the Solway arid Caledon ranges, the most important of these being Caledon Jade Green. Apart from the
fact that there was no really satisfactory green in the vat series before its discovery, it is outstanding because of its remarkable fastness, which is excellent in every way. This,
combined with its exceptional brightness, places it in the premier position among modem dyestuffs.

So far an approximate review has been given of the field of operations which the company has chosen in the development of the fast dyes.

In order to give some idea of the methods of manufacture of the colours a few examples are chosen below. Beginning with the acid alizarin colours, one of the most
important of these is Solway Green. This is prepared by the condensation of leucoquinizarin with p-toluidine.  Leucoquinizarin is itself prepared from anthraquinone in the
following stages:—

This is then condensed with p-toluidine and the product oxidised and then sulphonated.

As with many other dyestuffs, the major portion of the manufacture is concerned with the production of the necessary intermediates. Other methods have been used for the
manufacture of quinizarin from anthraquinone, but many of these yield mixtures of quinizarin with other hydroxyanthraquinones. More than forty different
hydroxyanthraquinones have been described, and the methods for the preparation of a single derivative free from the others are necessarily often complex.    

Starting with anthraquinone, sulphonation offers the most effective method of introducing a single substituent in the alpha position. Sulphonation of anthraquinone requires
oleum, and the sulphonic groups all enter in beta positions, but in the presence of mercury the alpha positions are occupied instead. A charge of 500 lb. of anthraquinone
requires about 160 lb. of free sulphur trioxide, which is added as the requisite quantity of 30-40 per cent oleum. Anthraqinnone is then added gradually through the manhole
in the lid with the stirrer going and then 1 per cent of mercurous sulphate. The cover is then put back on to the manhole and the pan heated to about 140° C during three
hours and kept at this temperature for 1 hour. After cooling it is blown into a vat containing 300 gallons of water; the water is then raised to the boil by blowing in live steam.  
Some of the anthraquinone remains unsulphonated and is filtered off through a filter press. If the sulphonation is carried so far that no anthraquinone remains
unsulphonated, a large yield of disulphonic acids is obtained. The recovered anthraquinone remaining in the press is washed and dried. The solutions from the press are
run into another vat and the dissolved acid is then salted out by adding potassium chloride or other potassium salts. Potassium compounds are as the potassium salt of
anthraquinone sulphonic acids is less soluble than the sodium salt   The potassium salt is filtered off and is preserved in the wet paste form, as it comes from the filter
press for the next operation, in which the sulphonic acid group is replaced by a hydroxy group by heating under pressure with alkali. The moist charge is transferred to an
autoclave. For this reaction a horizontal autoclave is generally employed. Water is added to the extent of twenty times the weight of sulphonic acid present (calculated as dry)
and calcium hydroxide to the weight of the anthraquinone sulphonic acid. The autoclave is then sealed, heated to 190° C., and kept at this temperature for 4 hours. The
contents are then blown out under their own pressure into a wooden vat full of cold water, made acid with hydrochloric acid, boiled and filtered. The product is obtained as a
bright yellow paste, which is then dried.

The hydroxy group, having been introduced in the 1-position, serves as a directing group for further substitution in the 4-position. This is carried out according to British
Patent 209,694 (Thomas and Scottish Dyes, Ltd.).   A jacketed stirrer pan is charged with 640 lb. of sulphuric acid of about 98 per cent strength, and to this is added 120 lb.
of  1-hydroxyanthraquinone. The temperature is raised to and kept at 70-75° C. until the 1-hydroxyanthraquinone has gone into solution. The charge is then circulated at 70-
75° C. through a tower connected to the pan and dry chlorine passed through at the bottom of the tower at the rate of 5—6 lb. per hour.  After 80 lb. of chlorine has been
passed in, a sample of the charge is withdrawn, and if analysis shows the chlorination is complete the crude l-hydroxy-4-chloroanthraquinone is precipitated by pouring into
water, filtered, washed free from acid and dried.  When, however, as in this case the l-hydroxy-4-chloroanthraquinone is required for conversion to quinizarin, a reaction which
is also carried out in sulphuric acid, the chloro body need not be isolated from the acid, but the next stage is earned out directly, 80 lb. of boric acid being added to the pan
and the melt heated at 160° C. for 12 hours. It is then isolated by pouring into water, filtering and so on. The qiiinizarin is obtained as a bright orange-red powder. A battery of
two chlorinating pans with towers, complete with the corresponding isolation vats and filter press is shown in Fig. 5.

It is reduced to leucoquinizarin by treatment with sodium hydrosulphite in alkaline solution or with aluminium powder in strong sulphuric-acid solution.

The quinizarin is reduced to the leuco form before condensing with p-toluidine in order to avoid the production of oxidation products, which result if quinizarin itself is
employed. A mixtureof 10 kg. of leucoquinizarin, 150 kg. of  p-toluidine, and 10 kg. of boric acid is heated at 130-140° for about 10 hours. A stream of air is then blown through
the melt to oxidise the condensation product (which is in the leuco form), and the melt is steam-distilled to remove p-toluidine. The precipitate is filtered off, dried, and is then
ready for sulphonation. The 1, 4-di-p-toluidinoanthraquinone is stirred into 10 parts of 10 per cent oleum at a temperature of 15—20° , and kept at this until a sample is
completely soluble in water. The whole melt is then poured into ten times its weight of water, salt added with stirring until the whole of the green colour is precipitated and
this then filtered off. The paste, which contains salt, is dried, and the color value of a sample determined in the dyeing laboratory.  According to the result obtained, more salt
or stronger colour is added to the product until it is brought to the right standard, and finally the mixture is ground in a mill. It is tested again after this, and if satisfactory is
passed to the stores department for packing and issue.

An examination of the various intermediates in the production of Solway Green shows the interesting fact that by the introduction of auxochromes into the practically
colourless anthraquinone, the colour is deepened to green. Anthraquinone itself has a faint yellow colour due to the presence of the two CO chromophores. On sulphonation
practically no colour change is produced, sulphonic acid groups having little effect in this connexion. On replacing, however, the sulphonic acid group by a hydroxy group, a
bright yellow is produced. The hydroxy group is one of the most important auxochromes, and in the alpha-position in anthraquinone deepens the colour to yellow. If
substitution is made, however, in the beta-position a much less intense colour is produced. On adding chlorine in the 4-position practically no change is produced, as
chlorine is similar in this respect to the sulphonic-acid group, but on replacing the chlorine by the hydroxy group, the colour is deepened from yellow to orange-red. The
colour of quinizarin depends to a certain extent on its state of division, and it can be obtained in shades from an orange to a scarlet, according to its method of preparation. It
will be noticed that the introduction of this second hydroxy group has produced approximately the same colour change as the first, and in fact a greater change here than
would have been produced in any position other than the “4”.

In Solway Green, both these hydroxy groups are replaced by p-tolylamino groups which are powerful auxochromes, and the change from red to green is obtained in one step.
If, however, the condensation is carried out under slightly different conditions it can be stopped when only one hydroxy-group has been replaced by the p-toluido group, and
the product has then a purple colour. If instead of replacing one of the hydroxy groups with p-toluidine it is replaced by the leas powerful amino group, a much less blue
shade results. Again, if in Solway Purple the remaining hydroxy group is replaced by an amino group, a product dyeing in greenish-blue shades is obtained, so that from the
examples given we can see a gradual deepening of colour from pale yellow through yellow,
orange-red, bluish-rod, purple and greenish-blue to green.    

As an example of one of the.Caledon colours, the manufacture of Caledon Brilliant Purple RR may be taken. The stages are as follows :—

It was discovered by Bally when applying the Skraup quinoline synthesis to beta-aminoanthraquinone that a second ring formation took place in addition to that through the
amino group, the resulting compound being:—

By working with anthraquinone itself, the corresponding derivative without the pyridine ring was obtained, and this compound, bcnzanthrone, on fusing with potash gives
dibenzanthrone, a blue vat dyestuff. This product was the first blue dyestuff for vegetable fibres (excluding mordant colours) which did sot contain nitrogen. In the production
of Caledon Brilliant Purple RR, the use of the chlorobenzanthrone in the potash fusion results in an isomeric condensation product of redder shade than dibenzanthrone.

Iso-dibenzanthrone to be converted into Purple RR requires chlorination.   This both brightens and reddens the shade. The chlorination (Fig. 6) can be carried out in a variety
of ways. The intermediates already mentioned have all been synthesised from anthraquinone, but in a few instances it is more convenient to synthesise a derivative from
phthalic anhydride by a modified Friedel-Craft condensation. An example of these is 2-methylanthraqninone. The corresponding 2-mefhylanthracene is present in coal tar,
but its extraction for technical purposes is not practicable. In addition there is no convenient synthetic method of introducing a methyl group into the anthraquinone nucleus.
The synthesis of this body from phtbalic anhydride and toluene with aluminium chloride, however, takes place very readily and with good yield. Condensation takes place
normally in the para-position to the methyl group. An excess of toluene is used as solvent, the toluene and phthalic anhydride being stirred together in a large iron pan and
the anhydrous aluminium chloride added in small quantities at a time. A rise in temperature takes place with this addition, but heating is applied towards the end to
complete the reaction.

The large quantities of hydrochloric acid given off during the reaction are recovered by passing through small absorption towers (Fig, 7). When the reaction is complete the
excess of toluene is distilled off and the product treated with dilute acid, which dissolves everything but the toluylbenzoic acid. This is filtered off and further purified by
extraction with an alkali. The dry product is then converted to the anthraquinone derivative by the usual method of ring closing with sulphuric acid. One of the most important
applications of this 2-methyl-anthraquinone is in the manufacture of Caledon Red BN.  The phthalic anhydride required for this purpose is manufactured by Scottish Dyes,
there being a complete plant (Figs. 8, 9) for this purpose. The method of production is by air oxidation.   Naphthalene is vaporised and passed with air over a heated catalyst,
the products being then condensed and purified by re-aubliniation. The product is obtained in very long white needles and is of exceptional purity. At the present time the two
factories at Grangemouth and Carlisle are working at full capacity, so that the establishment at Grangemouth has been fully justified.

As a measure of the development and achievement of the firm it may be stated that over thirty per cent of the colours marketed are new products, having no foreign
countertypes at the time of their appearance.  It is to this development more than anything else that the firm can claim an honourable position among the world’s dyestuff
Supplemental Information from ColorantsHistory.Org:
Anthraquinone Dyes Produced by Solway Dyes in WW I
German Type
Solway Trade Name
Date Produced by Solway
Indanthrene Yellow G
Caledon Yellow
Feb. 1915
Indanthrene Blue
Caledon Blue
March 1915
Indanthrene Dark Blue Bo
Caledon Purple
April 1917
Indanthrene Green B
Caledon Green
April 1917
Indanthrene Brown BB
Caledon Brown
April 1917
Indanthrene Red BN
Caledon Red
August 1917
Indanthrene Pink B
Caledon Pink
August 1917
Indanthrene Violet B Extra
Caledon Violet
August 1917
Alizarine Sapphirole
Solway Blue
March 1916
Alizarine Cyanine Green
Kymric Green
July 1917

1)  "What the British Have Done", American Dyestuff Reporter, Vol. 2, No. 7, March 18, 1918, p. 8
Click Here for History of British Dyestuffs Corporation and ICI
Click Here for Video on Discovery of Phthalocyanine at Scottish Dyes
History of Holliday Dyes and Chemicals
Report on Manufacturing Chemistry in the South Lancashire District-1861
Scottish Dyes Ltd.
Fig. 1 A Research Laboratory
Fig. 2 Some of the Chemical Houses
Fig. 3 A High-Pressure Autoclave
Click Images to Enlarge
Fig. 4 One of the Chemical Houses
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Fig. 5 Quinizarin Plant
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Click Image to Enlarge
Fig. 6 Chlorination Plant for Iso-Dibenzanthrone
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Fig. 7 Hydrochloric Acid Recovery Plant
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Fig. 8 Phthalic Anhydride Plant
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Fig. 9 Sublimed Phthalic Anhydride
Click to Enlarge
Solway Dyes Advertisement, The Times, 1917
Courtesy of Mr. Thomas Jackson.  Click to Enlarge
Scottish Dyes Ltd. Workers ca. 1920s
Biography of Dr. John Thomas, Chief Chemist of Scottish Dyes
History of Yorkshire Dyeware & Chemical Co.
Morton Sundour Advertisement, 1921
Handbook of the Upholstery and Allied Trades
History of Roberts, Dale & Co. in Manchester
New Book-90 Years On The Earl's Road by John Blackie (History of Grangemouth Works)
Biography of Robert Fraser-Thomson, Manufacturing Chemist for Scottish Dyes