Finishing

Purpose and Methodology

1.0 Finishing is the application of one or more coats of finishes or seasons to the leather

1.1 To improve the appearance, either by levelling the colour and hiding blemishes, or by providing a base for the production of a polish or gloss
1.2 To afford protection against moisture, oil and abrasion
1.3 To make the leather colour fast to wet and dry rubbing
1.4 To produce some special effect

2.0 Methods for Grain Leather

2.1 The Main Stages which may be used
2.1.1 Water Stain and fill
2.1.2 Stain (bottom coat)
2.1.3 Season (second coat)
2.1.4 Clear Season (top coat)
2.1.5 Fixative
2.2 Water stain and stain coats are often applied by pad (roller coater now more in use in the 1990s)
2.3 Later water coats are normally sprayed
2.3.1 hand spray
2.3.2 machine spray
2.3.3 curtain coater
2.4 Some put on 5- 6 coats with mechanical treatment (pressing etc.) in between
2.5 Some leathers only use a wax for water resistance and face

3.0 Preparing Leather for the Finish Coat

3.1. Always check the leather carefully before applying the finish
3.2 Setting - watch for creases
3.3 Trimming - watch for loose bits of flesh, for toggles, nails etc. in the leather
3.4 Leather should be flat
3.5 Fatliquoring - watch for dark patches, indicating uneven fat distribution. These will make the finish go on unevenly and create streaks if put on by hand, the finish will tend not to adhere, and the leather will go black on buffing
3.6 Similar problems will occur if fat is on the surface of the leather
3.7 Loose flesh must be removed by patch buffing
3.8 Over thick necks should be buffed down
3.9 If leather is firm it should be boarded
3.10 If neck is hard it should be slightly staked
3.11 If the fat distribution is OK it is fine to move on to finish full grain leather

4.0 Finish Films and Materials

4.1 Finish is any coating supplied to leather to protect the grain or for some other purpose
4.2 Generally the coating applied is thin (except perhaps wax coats)
4.3 Films usually give brighter surface (or face) to the leather after rubbing, plating, glazing or rolling
4.4 Materials:
4.4.1 Natural protein types Egg Blood Casein Glue
4.4.2 Natural and Synthetic Carbohydrate Gums and Mucillages Natural- Seaweed and Linseed Synthetic -Me cellulose
4.4.4 Resins Natural resins - Shellac Synthetic resins - Acrylate Butadiene also nitrocellulose
4.5 Casein
4.5.1 Protein from milk
4.5.2 The powder is soluble in weak alkali (e.g. borax)
4.5.3 Very fine casein powder does not disperse as readily as coarser types
4.5.4 Standard particle sizes are 30/60/100 mesh (number of particles per inch)
4.5.6 Gives a good clear film, but a brittle one
4.5.7 Plasticiser is used to prevent brittleness. (10%glycerine, TRO -Turkey Red Oil, Polyglycol)
4.5.8 TRO tends to keep the casein on the top of the leather
4.5.9 Glycerine tends to take the casein into the leather
4.5.10 Used as a binder for pigments
4.5.11 If solution is kept a long time, preservatives are required (two better tan one)
4.5.12 More viscous than albumen
4.5.13 Gives filled appearance
4.6 Albumen
4.6.0 From egg or blood
4.6.1 Heat sensitive
4.6.2 Comes in flakes or bulbs (I have only used flakes)
4.6.3 Dissolved by soaking in water, stir overnight at no greater than 30degC, disperse the following morning 4.6.4 There is a danger of overheating while dissolving
4.6.5 Examine for excessive non-solubles before use
4.6.6 Ammonia(NH3) or diethylene glycol in small quantities helps dissolving
4.6.7 Clean the container before use
4.6.8 Nitrobenzene or HCHO used it goes bad
4.6.9 Plasticiser always used
4.6.10 Blood is cheaper than egg
4.6.11 Black blood (not defibrillated) is used purely for cheapness on poor leather
4.6.12 Make up materials to 10%
4.6.13 Solid content should end below 2%
4.6.14 Egg does not give the filled appearance that casein does
4.6.15 Egg is limpid compared with casein
4.6.16 Casein, egg, and blood can be mixed to suit the absorbency of the leather
4.7 Seaweed Mucillages
4.7.0 Algin extracted from laminaria with caustic soda
4.7.1 Colour of algins are from browns to colourless
4.7.2 Irish Moss is very useful (trade name Blandola)
4.7.3 Bought dry in bales
4.7.4 Now provided as 2% jelly
4.7.5 A 4% jelly would almost stand upright
4.7.6 May contain Mg, Ca salts which can interfere with other parts of the finish
4.7.7 TRO is used to sequester these salts
4.7.8 TRO is also a good plasticiser
4.8 Linseed Mucilages
4.8.0 Seeds are boiled in water for 2 hours
4.8.1 Strained while hot
4.8.2 Care is taken not to break the seeds as mucilage comes from the husks
4.8.3 Good medium for dye
4.8.4 Does not look as though it has been stuck on the leather, rather a part of the leather
4.9 Mucilages
4.9.0 Mucilages fill the leather
4.9.1 Mucilages protect, enhance the grain
4.9.2 A simple finish: protein albumen plus casein plus mucilage. Is not fast to water or to spotting.
4.10 Shellac
4.10.0 From small insects (tree insects) - Laccifer Luca. Shellac is a resinous exudation
4.10.1 Found in east India and Thailand
4.10.2 The branches containing insects are removed and boiled
4.10.3 There are about thirty varieties - some crude, some refined
4.10.4 Main component is a complex mixture of high Molecular Weight hydroxyacids
4.10.5 Sometimes contains wax which acts as a natural plasticiser
4.10.6 Some are adulterated with rosin - comes as dark colour
4.10.7 Bleached Shellac is bleached with hypochlorites - it becomes insoluble with ageing and film forming properties and water resistance of film is impaired
4.10.8 Shellac is insoluble in water (HOH), but being acidic is insoluble in weakly alkaline solutions - was therefore emulsified
4.11 Synthetic Resins
4.11.0 Acrylate was first made as a permeable undercoat for nitrocellulose
4.11.1 Acrylate finishes are thermoplastic
4.11.2 Acrylate finishes can be dissolved by solvents
4.11.3 Sometimes toe puffs softened in solvent (methyl acetate). If puff put on too wet the solvents may attack the acrylate in the finish of the upper leather
4.11.4 The Toe Puff in a shoe is normally thermoplastic
4.11.5 Acrylates plastic rather than elastic
4.11.6 Other man useful resin since 2nd World War: dienes
4.11.7 Dienes are elastic rather than plastic
4.11.8 Acrylates superior to dienes in light fastness
4.11.9 Can add a stabiliser to dienes, but other additions can upset the film
4.11.10 Dienes are superior to acrylates in wet rub
4.11.11 The smaller the particle size the greater the penetration (this is generally true for all films)
4.11.12 After the war cellulose only used on special leathers as wide variety of resins available
4.11.13 Discontinuous films are required with resins available
4.11.14 Therefore add casein or wax emulsion, or linseed, which do not form continuous films with acrylate 4.11.15 These additions tend to harden film
4.11.16 Resin Finishes should not be allowed to freeze, as this produces irreversible changes
4.11.17 Sometimes manufacturers will not deliver in cold weather if they have no insulated lorries
4.11.18 Resin finishes internally plasticised give no trouble with kekkyness
4.12 Waxes
4.12.0 Waxes give a polish
4.12.1 Aid spot resistance
4.12.2 Carnauba wax (melting point 84deg F) is the best wax
4.12.3 Carnauba wax is very expensive
4.12.4 Yellow carnauba best for hard films
4.12.5 Grey carnauba is good enough for mixing with finishes. Grey is a fatty type
4.12.6 Carnauba is a vegetable wax
4.12.7 Carnauba is sometimes adulterated with candilla wax (also vegetable)
4.12.8 Gersthofen wax (BASF) is synthetic, but not so good as the vegetable
4.12.9 It is easy to make a was emulsion with ordinary soap, triethylamine soaps, or non-ionic emulsifiers (e.g.Lubrol w from ICI or Emulphor E from BASF)
4.12.10 Small amounts of micro crystalline wax is used in was to modify it and make it softer
4.12.11 TEA soap is best emulsifier as wax dissolves giving a very clear film
4.12.12 All above waxes similar to varnish, protecting, beautifying and shining
4.12.13 All an be tinted with dyestuff but cannot hold too much dye or it will rub off.
4.13 Pigments
4.13.0 Pigments came in in 1918
4.13.1 With original coats (casein etc.) pigment ground hides defects, levels the colour.
4.13.2 With the very best dyed leather you normally see a slight variation between butt and belly
4.13.3 White - TiO2 (Titanium dioxide) Brown - Iron oxides Yellow - lead chromate Orange - basic lead chromate or ferrite lemon yellow Black - black iron oxide, carbon black Green - chromic acid, chrome oxyhydrate,synthetic organic pigments Blues - synthetic organic pigments Reds - synthetic organic pigments 4.13.4 Organics are not volatile and fast to light
4.13.5 When using pigments you must know what type of finish is required
4.13.6 Do not mix more than one range of pigment finish. Mixing various types will give rise to errors
4.13.7 Aqueous pigment finishes are dispersions of pigment in aqueous media including casein (with or without the addition of shellac), wax, gelatine, mucilage, and plasticising oil
4.13.8 Inorganic pigments have a particle size greater than organic
4.13.9 Pigments, unlike dyestuffs, are insoluble in water or solvents
4.13.10 Pigments are opaque
4.13.11 Pigments have a hiding and obliterating power e.g. paints
4.13.12 Pigments are prepared by grinding natural, coloured rocks or ores to fine powders (e.g. iron oxides) or by roasting ores (Titanium dioxide), or by chemical preparation (lead chromate)

5.0 Putting Films on Leather

5.1.0 The film must not be too thick to detract from the appearance and the quality of the leather
5.1.1 The finish on the leather must be satisfactory to wet rub and dry rub
5.1.2 The finish must be capable of easy application by pad - no streaks, or by spray - evenly spread
5.1.3 The finish must adhere well - not powder or split
5.1.4 The finish should cover defects as required
5.1.5 Films must be designed in accordance with the way they will be used and completed on the leather. These will include such things as being: a. Matt or lively b. capable of being glazed c. capable of being brushed to a bright face d. resistant to hand ironing
5.1.6 Upper leather must be capable of getting through the shoe making process. This includes being able to be pressed without sticking to the plate
5.1.7 The finish, for all end uses, will need to be fast to light
5.1.8 The finish should not deteriorate with age
5.1.9 Finishes cannot improve the break of leather, only damage it
5.1.10 Put on as thin a film as possible
5.1.11 Finish films should have a secondary flow which evens them out
5.1.12 If leather is too absorbent this secondary flow cannot occur
5.1.13 To thicken a film add thickening agents or remove water
5.1.14 To thin a film a.add water, or b.add essential oil, or c. add alcohol, or d. add wetting agent (wetting agent tends to be disliked as likely to persist in the film and effect the finish qualities) or e. use two coats of the original film
5.1.15 With inorganic pigments there should not be problems of light fastness, except some yellows and oranges can darken
5.1.16 Adding dyestuffs to finish risks poor light fastness and wet rub troubles
5.1.17 Finishes should not be soluble in solvents such as those used in cellulose oversprays
5.1.18 Finishes must age without deterioration
5.1.19 Hardness (kekkyness) is caused by migration of plasticiser. The plasticiser is absorbed by the leather giving a hard finish on top.
5.1.20 Resin finishes are internally plasticised and should give no trouble with kekkyness
5.1.21 The best finishes are not continuous but look microscopically like dried mud. Continuous films tend to crack and give bad break.
5.1.22 The smaller the particle size the greater the penetration
5.1.23 The film that goes in well has good adhesion
5.1.24 The film that stays on top may tend to peel off

6.0 Making Finishes

6.1.0 Unpigmented finish formulation
6.1.1 Wax emulsion largely for top season binders
6.1.2 24lbs yellow carnauba 3/4 lb ceresin wax 48 ounce sulphonated cod oil 12lbs soap flake in 12 gal water at 95 degrees C (flanola good soap flakes) put whole thing through a milk cooler
6.1.3 Soap gives good filling properties
6.2.0 Glazing leather
6.2.1 Use protein, blood, small amounts of shellac
6.2.2 Fresh blood from slaughterhouse is preferred but hard to keep. Must clean the barrel, wash with formaldehyde, run round with a little benzene. Blood will then keep well.
6.2.3 1% ammonia on albumen assists dispersion
6.2.4 Casein, egg, blood, glaze well. They are not fast to rubbing and have to be fixed
6.2.5 Can add shellac but it melts on glazing
6.2.6 Top season after 1st glazing with large amounts of albumen may give more brilliance after 2nd glaze
6.2.7 Casein, shellac, blood and egg are film forming; to which are added plasticiser, fillers, and lubricant
6.2.8 For glazed leather generally: 8oz of egg albumen, 9 pints milk (contains cream - 32% fat), 3 gallons water
6.2.9 also for glazed leather: 100 casein 10 deg C, 60 milk, 320 water
6.2.10 also for glazed: 250 sodium alginate 2%, 40 milk, 80 blood albumen 10%, 30 water
6.2.11 A little dye can be added to
6.2.8, 6.2.9, and 6.2.10 6.2.12 Box lustre: 40 water, 9 casein, and 2 borax added to 10 water, 10 fish glue, 7 D.E.G.
6.2.13 Also: 2and 3/4 lbs borax plus 2 and 1/2 gallons stirred, dissolve the borax, add casein and apply steam. 12lbs casein plus 3 and 3/4 lbs TRO. (highly sulphated castor oil). Excessive TRO but often excessive to get better film
6.2.14 And also: 70grams water, 4p Ammonia 880, 14 lbs shellac all mixed and then add 1/2 gallon diethylene glycol

7.0 Flesh Finishes

7.1.0 These include mulches, boshes, and moss backing
7.1.1 Designed to close flesh up
7.1.2 The film must be evenly penetrated and bend with the leather in the same way as the grain. If the film goes in too far the flesh fibres will stick out and still be loose. If the film sits in the surface it will not bend with the leather. Penetration is a matter of finish viscosity.
7.1.3 Finish penetration is also affected by plating, and/or fluffing then plating, and/or a light bosh, fluff, clean, and a second coat (if leather very absorbent)
7.1.4 For chrome splits use either an acrylic binder or rubber latex plus a strong mucilage (this is much cheaper)
7.1.5 Can buy a made up formula
7.1.6 Example finish: 30gram soap flakes in 8 gallon of water plus 13gram of methyl cellulose (450 viscosity in 8 gallon) a. thin for light leathers, b. not at all water resistant, c. for heavy leather splits, sole leather, dressing leather, some kips
7.1.7 Another example for wallet leathers: 2 parts casein 12%, 6 parts water, 1 part m/c 2500 v 2%, 1/2 part shellac all with 1% HCHO when spraying

8.0 Pigmented Finishes

8.0.1 Very often binder with the pigment ground in. BOUND - PASTES - DISPERSION - POWDER
8.1.0 Bound
8.1.1 Balanced mixture. Casein, shellac - wax 10% - 15% pigment
8.1.2 Lot of binder
8.1.3 Very thin: easy to measure out small quantities of pigment
8.1.4 Normally used in vegetable, semi chrome to get a lot of binder in. (for resins you want the minimum amount of binder)
8.1.5 10% pigment finish (by volume) must be added to get even colouring
8.1.6 Some can be glazed
8.1.7 Not fast to wet rub
8.1.8 Cannot be fixed
8.2.0 Pastes
8.2.1 Most common by far
8.2.2 Thick
8.2.3 Casein plus oil
8.2.4 20-30 per cent pigment
8.2.5 Put on spray, glaze
8.2.6 Then season 100pts glaze lustre, 50 blood, 5 TRO, made up to 1000 with water
8.2.7 Then plate or hand iron
8.2.8 Formulation: 100pts paste pigment (organic or earth colours), 30-50 glazing lustre ( casein - a casein plus fish glue), 5-10 parts paraffin emulsion, to 1000 parts with water
8.2.9 Dyestuffs are not desirable with these (not rub fast)
8.3.0 Dispersion
8.3.1 Thin (strong - apt to sediment, which it should not - depends on dispersion agent)
8.3.2 Must be constantly stirred
8.3.3 Contains little or no binder
8.3.4 40-60% pigment
8.4.0 Powder
8.4.1 Mainly exported
8.4.2 Made with casein plus pigment plus borax and grind
8.4.3 Or do this damp and dry out rather than grind
8.4.4 Very good to export to hot countries where a great danger of evaporation
8.4.5 Bottom finish for unglazed leather: 40 wax (carnauba), 100 bound pigment, 25 plasticiser (TRO/Glycerine/OEC - 1/1/1), 100 water gives excellent cover with poor stock

9.0 Troubles in Pigmented Finishing

9.1.0 Putrefaction
9.1.1 If finish diluted (pH reduced: concentration of antiseptic reduced)
9.1.2 Antiseptic should be not less than 0.1%
9.1.3 pH should not be less than
9 9.2.0 Settling
9.2.1 All apt to settle
9.2.2 Especially so if diluted
9.2.3 Test by putting some in a cylinder overnight
9.2.4 Sometimes redisperse by stirring
9.2.5 Sometimes the settled material goes hard (return to supplier or get new supplier)
9.2.6 Sometimes settle in layers which are very hard to disperse a. make the finish more viscous b. add ammonia
9.2.7 Sometimes you get coagulation when stirring
9.2.8 Never add HCHO
9.3.0 Freezing
9.3.1 Produces reversible changes in resin finishes
9.3.2 Some manufacturers will not deliver in cold weather if they do not have insulated lorries
9.3.3 Precipitation of resin often brings down pigment as well
9.4.0 Incompatibility
9.4.1 If not compatible check pH of each
9.4.2 Raise the pH of lower to that of the higher
9.4.3 Use ammonium hydroxide
9.5.0 Foaming
9.5.1 Very complicated
9.5.2 Foam gives difficulties with spraying, curtain coating and the like
9.5.3 Foam reduced with alcohol or something which will evaporate off rather stay in the finish
9.5.4 If two finishes apparently equal always choose one which does not foam
9.5.5 Foaming is sometimes caused by beating air into the mixture
9.6.0 Hard Water
9.6.1 Can upset finish
9.6.2 Sometimes obvious, sometimes not
9.6.3 Check by making finish up with distilled or soft water
9.6.4 Threshold softening done with EDTA or Calgon
9.7.0 Foreign Bodies
9.7.1 Jam the guns on spray machines
9.7.2 Gives the leather a rough, harsh feel
9.7.3 Filter with nylon
9.8.0 Containers
9.8.1 Prefer plastic or stainless steel
9.8.2 Galvanised not recommended
9.8.3 Enameled liable to chip
9.8.4 Aluminium suspect in alkaline conditions
9.9.0 Application
9.9.1 No padding machine does the job properly. 1-2 operators are needed to smooth off afterwards
9.9.2 Streaking is caused either an over absorbent leather or a very non absorbent leather
9.9.3 Usual streaking comes from the over absorbent leather and can be overcome by plating before padding, thickening the finish, and/or juggling with water content It is also possible to give 2 coats the first with weak soft resin (5% solids) and the second covers
9.9.4 Sometimes a supplier may send two supposedly identical resins but with different particle size. The larger particle size will penetrate less
9.9.5 If the first coat is too resistant the second will not adhere. May be caused by plating being too long or too hot after the first coat. Or there may be too much wax in the first coat.
9.9.6 Excess wetting agent in the first coat may make the first coat too wettable. Also caused if the first coat is not thoroughly dried
9.9.7 Streaking may be caused by padding down too far - effectively by working the finish too dry

10.0 Corrected Grain

10.1.0 First Coat
10.1.1 This is a vital coat
10.1.2 Decides the character of the final leather
10.1.3 The leather must be correct
10.1.4 The coat must penetrate correctly - bind the fibres together
10.1.5 The softest resins possible are used. (use harder resins for scuff resistance, and water resistance, later)
10.1.6 The covering power of pigment is important
10.1.7 Pigment particle size is important. Inorganic is greater than organic. Consequently inorganic gives greater cover.
10.1.8 The transparency of the film is modified by the choice of pigment and the pigment/binder ratio
10.1.9 The selection of the leather must be modified according to the colour used.
10.1.10 Use as little pigment a possible
10.1.11 If you over bind your first coat with white it soon becomes yellowy
10.1.12 1st Coats Calf Corrected Black White Glove Case Resin Binder/Pigment M(med) 1.35 S(soft) 1.5 S+M 1.0 M 0.9 S+M 1.2/2.5 S+M 2.0 2nd Coat Resin B/P M+A(acrylate) 1.2 M+A 2.5 1.0 1.2 M+H(hard) 3.0 3rd Coat Resin B/P H 1.9 H+M 1.2 M+H 3.0
10.1.13 For Case leather the second coat will be abrasion resistant, with little bending or flexing
10.1.14 For Case leather the 3rd coat may often include casein
10.1.15 The first coat Binder/Pigment ratio is
1.1/1.2 for semichrome, softie, and lining
10.1.16 For the first coat on splits it is 2.3
10.2.0 Splits
10.2.1 Splits are tricky to finish
10.2.2 The finish sometimes surrounds the fibres and leaves them sticking up
10.2.3 After a few weeks aging the finish then fails
10.2.4 To avoid this, buff or use a mucilage or weak soft resin first coat
10.3.0 Moss Backed Splits
10.3.1 Pigmented - reduces elasticity of film
10.3.2 First coat filling, hen second with a little pigment.

11.0 The Customer

11.1.0 Break
11.1.1 Cardboard break must be avoided
11.1.2 Cardboard break can be obvious early on or can appear after aging if the plasticiser migrates
11.1.3 This latter happens if large amounts of plasticiser is used (not recommended) or if the plasticiser is overcome by the fatliquor - if large amounts of mineral oil used or only sulphonated oils
11.1.4 Bad break can be caused by overbinding the film with pigment
11.1.5 A pigment finish with a lot of Turkey Red Oil added must be watched. The pigment may be internally plasticised.
11.2.0 Butadiene resins are apt to oxidise and crack. Some splinter like glass after six months.
11.3.0 Finish should be even all over
11.4.0 Protein is fixed with formaldehyde (HCHO) and with Chrome acetate
11.5.0 For a good wet rub it is important to get the 1st coat right and to build on that.
11.6.0 If the dry rub is poor go for harder resins.
11.7.0 To get heat resistance put hard material on the bottom and build on that
11.8.0 If you get discolouration in white and pastels a. the fatliquor may be wrong b. loose vegetable tans may be migrating to the surface c. Do not scour or use sumac in the retan. Chlorophyll will come through d. lead chromates may give trouble
11.9.0 In shoemaking solvents are used and some resins are more resistant than others, Toe puffs in shoe making using ketones and acetones can destroy adhesion film in the leather (proteins are not affected)
11.10..0 For resistance to cracking in the cold the thickness of the film can be important.