Northern Renaissance Instruments

6 Needham Avenue, Chorlton-cum-Hardy, Manchester M21 8AA, U.K.

Phone & Fax. +44 (0) 161 881 8134; proprietor: Dr. Ephraim Segerman [USA]

e-mail: post@nrinst.co.uk; on internet: http://www.nrinst.co.uk

VARNISHING MATERIALS

Reg Lawrence and Ephraim Segerman

Revisions: Text February 1996, Prices valid 2009

The goal of NRI's research and development on instrument finishes is to convert the historical information that various researchers have collected (by analysing original finishes and studying early formulas) into practical finishing materials.

Reproducing the instrument finishes of the Old Masters is impossible in detail. No one can even be sure about what they looked like when new, and that appearance may not be acceptable today. We can only do our best to produce practical realisations of modern theories about them that we think make some historical sense. For the bulk of our finishing products we use those materials available today that most closely approximate the materials that the theories indicate were used then. We also offer modern additives that make the job easier and don't significantly affect the character of the final result. Included also are a few useful products that are not easily available elsewhere.

PINE RESIN VARNISH FORMULA A, FORMULA A.9 AND FORMULA A.5

For composition and characteristics see Oil Ratios and Colour sections of GUIDANCE ON USE

VARNISH LEVELLING ADDITIVE

A small amount of this additive, mixed into any oil varnish, helps it to go on smoothly. It works by reducing the surface tension, and more importantly, variation in the surface tension of the varnish. It allows very thin coats of high colour density to be put on evenly with less skill and effort. Brush marks flow out and the thickening of varnish around dust particles is greatly reduced. It is a modern chemical made up of fluorinated alkyl ester.

The additive is supplied as a thick syrup. It needs thinning with the varnish solvent (turpentine or white spirit) before it can be handled conveniently. (By leaving this to the user, we save the added costs of extra weight and special packing of flammable materials).

Add 3 parts of solvent to one part of additive. The solution will keep indefinitely. Either keep it in a tight container so no solvent evaporates, or mark the level of the remaining material on the bottle after each use so that evaporated solvent can be replaced before the next use.

Add the additive solution to the varnish so that the final concentration of additive in the varnish is between half and one per cent. To achieve this, mix one part of prepared additive solution into between 24 to 48 parts of undiluted varnish. We suggest you experiment to find how much leveller you need for best results. More than 1% does not increase the levelling effect. Much more than 1 % can lead to undesirable effects. You may also find that the amount of additive needed can vary from batch to batch of our varnish. This additive does not affect the keeping qualities of a varnish in any way that we know of. Yet it can make sense to delay adding it if one is storing the varnish for months or years. Like wine, the properties of our varnish improve with keeping. On maturing, clarity improves, and it often spreads very well without any additive.

HARDENER

This is an additive that speeds up the drying of NRI or any other oil varnish. It is a traditional hardener (including lead) except that its properties are improved by the addition of cobalt. For instruction on its use see the Drying section of GUIDANCE ON USE.

POTASSIUM SILICATE WATER GLASS

Potassium silicate water glass is better suited to instrument making than the more common sodium silicate water glass because it does not form the opaque patches that sometimes occur on a sodium silicate water glass surface while drying (caused by interaction with carbon dioxide in the air). It can be applied neat or diluted with some water.

The adhesion of varnish to water glass is excellent once both are thoroughly dry. But this adhesion can take many weeks to develop. Though the water glass appears dry in a matter of hours, residual moisture and the alkalinity it carries can affect drying of a varnish coat on top. It helps if one lets the water glass dry in a low-moisture atmosphere for several days before putting varnish on. We also recommend a thin layer of protein (eg. egg white or casein or glue) between the water glass and the varnish. This avoids unusually slow drying of the first varnish coat, and improves the initially poor adhesion that makes the varnish chippy for some time after application.

ROSIN OIL

Rosin oil is made from the distillation of Rosin. Alternative names for Rosin are Gum Rosin and Colophony. Rosin is the residue after turpentine is distilled from the sticky fluid collected from tapping pine trees. When the Rosin is distilled at about 350 degrees C., three types of Rosin Oil come out. The first type to come out flows very easily. It is opaque because it contains water (including some acid) from some chemical decomposition. The name Rosin Spirit is sometimes used for this type. The second type to come out is an almost-clear thick liquid, sometimes called Kidney Oil. The third type to come out has a darker grey-brown colour than the second, and is rather thicker (with a treacle-like consistency). It is sometimes called Bloom Oil.

Thin films of the Rosin Oils will harden with time, the third type taking a few days and the others progressively longer. The hardening can be considerably speeded up by additives. For instance, adding our Hardener in the same proportion as in a varnish (1 or 2 drops per teaspoon) makes a thin coat of the second or third types dry to touch overnight. The mechanisms of hardening and acceleration of hardening are not chemically understood, but if it involves polymerisation, it is a different process from the "drying" of oil varnish, which involves oxidation. It could be solidification of a supercooled liquid.

The viscosities of the three types of Rosin Oil greatly affect their penetration of wood. A brushed application of the first type will often penetrate through to the other side of a violin rib. To limit this penetration, a light wipe with a cloth wetted with the oil is recommended for the first type. The method of application for the other types is not so critical, but bathing the surface with the oil is to be avoided. If an oil is too viscous to handle effectively, warming will reduce the viscosity. If one wants greater penetration of the more viscous Rosin Oils, one can thin them with turpentine or white spirit.

The index of refraction of Rosin Oils varies from about 1.50 to 1.55, with the first type at the bottom of this range, the second in the middle and the third at the top. The index of refraction of wood is also in this range, and this explains the extraordinary optical properties of Rosin Oil. The surface between a wood fibre and a Rosin Oil coating does not scatter the light falling on it. One literally looks into the wood fibre, and this gives the visual impression of depth that is considered so attractive, especially on figured woods.

Condax (CAS Newsletter 37 (May 1982), p 31) has suggested that the "ground varnish" of old-master violins, was hardened Rosin Oil. For such a complete layer of Rosin Oil, the second or third types of Rosin Oil seem to be indicated. The technique involves applying the oil, letting it harden, and then sanding or scraping it down to the wood surface. Rosin Oil is very stiff and so should be beneficial to the instrument's acoustics. It is not advisable to leave much thickness of Rosin Oil on top of the wood surface since it is brittle and not as resilient as varnish when in a continuous film. It is a sealer but not a filler in the sense that it is good to leave thick patches to fill dips in the wood surface. We recommend doing the filling with a subsequent coat of A.5 varnish.

More recent research at Cambridge University indicates that the ground layer on most Old Master violins is primarily a fine mineral powder (possibly volcanic ash) apparently in some medium that is suspected to be Rosin Oil. Such a layer both seals and fills (in fact, the ground layer is considerably thicker than the varnish layer in some areas).

Some modern makers are just coating the wood fibres with a light treatment of Rosin Oil to get the optical effect, and then completing the ground coat with some other material. For this approach, any of the types of Rosin Oil seems to be appropriate.

Some makers are adding Rosin Oil to varnish of their own making to improve clarity. Traditionally Rosin has been used for this, and such varnishes have a tendency to craze with time. Only Rosin Oil I could possibly still retain whatever components are responsible, but we expect that these are decomposed in the distillation.

STAND OIL

This is made by boiling linseed oil with no oxygen present until it is very thick (highly polymerised). It is used in our varnishes because it dries much faster than ordinary linseed oil. We have found that, compared to varnishes, waxes and other oils in thin layers, Stand Oil provides the best barrier to the passage of moisture vapour in a natural product. It therefore seems appropriate to use it for sealing the insides of instruments to promote stability of the wood against humidity variation. Stand Oil, in a thin layer before varnishing, can be used to provide a sheen in the appearance of the varnish. It can be thinned with solvent (turpentine or white spirit) for application. Hardener speeds drying. Double the amount used normally in varnish is appropriate. It can also be used to make A.9 varnish out of A.5 and A out of A.9. See the Oil Ratios and the Violation of the Lean-to-Fat Principle sections of GUIDANCE ON USE for further discussion on these uses. Stand Oil is also useful for those who make their own varnishes.

MADDER RED PASTE

This paste is the active principle of madder root mordented onto talc dispersed in a small amount of our clear varnish. Some of our customers use it in their experiments.

TACK RAGS

These are made by impregnating lint-free cloth with a non-drying oil that is compatible with all paints and varnishes. When wiped over a dry surface the amount of oil is just enough to make dust particles stick while leaving an insignificant amount of oil on the surface. Tack rags produce a dust-free surface to varnish over and save time picking up nibs.

NYLON FILTERS

There are various circumstances under which particles can get into varnish. If one suspects that this has occurred, one can filter the varnish. The specification indicates that the square holes in the filter are about .08 mm (.003 inches) in size. It is theoretically possible for a particle that is noticeable on close examination of a dried varnish layer to get through this filter, but this is rare in practice. After use, the filter is cleaned with solvent as one cleans brushes.

PLASTIC DROPPER PIPETTES

These are for transferring small quantities of liquid from one container to another. Not everything modern chemistry offers is high-tech and expensive.

GUIDANCE ON USE

There is a wide variety of varnishing methods and strategies which work for their users and lead to good-looking instruments. There is no intention here to prescribe any 'best' methods, though as often as we can, we refer to observations of the methods of the Old Master instrument makers. This leaflet contains the answers we offer to questions we often get asked by both experienced varnishers who are trying our varnishes for the first time and students with very little varnishing experience. It may be considered inadequate by the experienced varnisher because it is not comprehensive, and by the beginner because it is not a step-by-step do-what-you're-told instruction manual. Nevertheless we hope that all will find it useful and informative.

PRE-VARNISHING WOOD TREATMENT

There have been various theories about treatment of the wood before the Old Masters made it into instruments. The modern tradition is just to let it mature for 5 years for the good tone to develop. An additional hundred or more years helps. The idea of a long soak in cool water has been shown to be very unlikely by recent research at Cambridge University. But there is evidence that some treatment, probably 'salting', was used on fresh wood to avoid woodworm and reduce the amount of movement with changing moisture content, and in the process to greatly accelerate maturing. It probably involved stewing the wood in a salt solution. Theoretically, the heat and water should improve the wood by reducing the amount of hemicellulose present, the main effect of aging. With enough stewing of the wood, a good modern violin can sound and feel remarkably like an Old Master one (as to how much is enough, the Stamm criterion of 1% loss of dry weight per century of aging is probably relevant).

Once the woodwork on the instrument is finished, and before varnishing with colour, one usually treats the surface with chemicals to make the wood more attractive, or to perform other functions, which include to stiffen, fill, seal, protect against abrasion and dirt (after varnish has rubbed off and before revarnishing), and facilitate varnish removal prior to revarnishing. These will be discussed below in the order mentioned here.

Some modern makers like to colour the bare wood bright yellow with a material like gamboge. Others like to approach the yellowish-tan look of Old Master instruments (where the varnish has rubbed off) by applying a considerable dose of ultraviolet light from the sun or a UV cabinet, or brushing on a mild colourant such as tea. Some enhance the colour contrasts of flamed wood with a very light wipe of coloured varnish. The visual impression of depth on the wood surface is considerably enhanced by the application of a transparent material of high index of refraction. Such materials are Rosin Oil, Potassium Silicate Water Glass and Clear Varnish (especially Formula A.5).

All of the last three materials mentioned above are excellent stiffeners of the wood surface. The main function of a wood stiffener is to mechanically reduce the amount of expansion or contraction of the wood with changing humidity in its environment. Such wood movement changes the action, changes plate tuning and strains joints. The stiffener should be most effective if it locks the wood in its swollen state. Another function of a stiffener is to raise the resonant frequency of the wood. Since each resonating part of an instrument has ideal resonant frequencies in its design, if the wood has been stiffened, these frequencies can be achieved by carving the wood thinner. Less wood means less sound absorption, so this should lead to more sound output.

Surface irregularities show up much more clearly when a surface is shiny than when it is not. So somewhere in the finishing process unobserved unevenness on the bare wood surface needs to be filled and smoothed by cutting down a thick layer. Some makers leave this operation to the end, sanding the surface of a thick top coat of clear varnish to smoothness. Whether they do this or not, most makers do this on a 'ground' coat before applying colour. This works well with Water Glass and Formula A.5 Clear Varnish, but with Rosin Oil, we recommend that this is done on a Clear Varnish coat on top of it. A furniture filling technique that goes back at least to the 19th century is to cover the surface with a thin layer of fine plaster of paris and to scrape or sand down to the surface again, leaving islands of plaster in the dips that needed filling. These islands disappear (visually) when varnish is applied and diffuses into the plaster because the index of refraction of the plaster particles matches that of the varnish well enough. Some violin makers do this by substituting a gel of very fine montmorillonite (also known as bentonite) particles for the plaster. Very finely ground glass or silica in a binding material like Rosin Oil should do very well For a filler the Old Masters used a finely powdered mineral (volcanic ash can come that way) bound in a material that the Cambridge researchers suspect is Rosin Oil.

Liquids penetrate bare wood mainly through pores which are in the grain direction. So when a colour is applied to it, the degree of colouration in each area depends on the surface concentration of end grain. This doesn't look bad with yellow, but darker colours can lead to a very blotchy appearance. Thus the pores need to be sealed before varnishing with colour. Some makers seal with linseed oil and others with animal glue (Maggini used the latter, according to Sacconi). The above fillers work as sealers, but the process of cutting down to smoothness might leave some exposed pores at high points. So a sealing coat of un-cut-down clear varnish is usually applied before colour.

Most fillers and sealers protect the wood against abrasion and dirt after the varnish has rubbed off and before revarnishing, but we doubt whether any other is as good as the mineral layer the Old Masters used. That surface is so good that it has become fashionable nowadays not to renew areas where colour varnish has worn off. But with relatively new instruments, and if a serious mistake is made in making or finishing, revarnishing is sometimes necessary, and one has to get the remainder of the old varnish off. Scraping it off is a lot of work and it has to be sealed and filled again. It is convenient to soften the varnish with a strong solvent and then wipe it off, but to avoid blotches, the sealing must remain intact. So the sealer must not be affected by the solvent. Minerals (including Water Glass) and glue do this well. This is the main reason why we do not recommend the very simple procedure of starting with A.5 Clear Varnish on the bare wood.

OIL RATIOS

All NRI varnishes are oil varnishes contain pine resin, linseed oil and about 10% turpentine. William Fulton has published a method of making such varnishes in the Strad (Dec. 1974). The oil to resin ratio of Fulton's varnish is 150 ml of oil to 100 gm of resin. This is equivalent to a weight ratio of 1.4 to 1. Let us call this an oil ratio of 1.4. This makes a very strong flexible varnish resistant to abrasion and chipping. For years we have been calling this our Formula A varnish. However, it takes some months for the varnish to harden properly, during which time the adhesion to the wood steadily increases. When first dried it will be found that the varnish can be somewhat 'chippy' and the surface can take an imprint of whatever it rests on for some length of time. We recommend that for the first few months after varnishing with Formula A the instrument should be left to hang freely suspended from its tuning pegs when not in use, and one should be particularly careful about avoiding knocks.

We have found that if the total varnish coating is kept to about 2-3 thousandths of an inch thick, an oil ratio of 0.9 has considerable advantages. We call this our Formula A.9 varnish. It is somewhat harder and stabilises far more quickly than our Formula A. Both harder and softer varnishes are observed on the best Old Master instruments.

A clear varnish with an oil ratio of 0.5 is ideal for first coats. It is quite stiff, dries very fast and is particularly easily sanded. This varnish, called our Formula A.5, is appropriate for use under subsequent coats of Formula A.9.

An ancient and wise tradition is that one varnishes from 'lean' to 'fat'. This means that the varnish layers should go from a low oil ratio at the wood surface to a high oil ratio at the outside surface. The reason for this is that the varnish layer in contact with the wood will have to move with the wood as the wood expands or contracts with varying moisture conditions, and if the outer layers are stiffer than the inner layers they will crack or craze when the wood expands, or wrinkle when the wood contracts. Formula A varnish (with oil ratio 1.4) is so flexible that these problems will not occur if it is used for all of the varnishing, no matter how thickly it is applied. One can be sure that these problems will not occur with our Formula A.9 varnish only if one keeps the varnishing thin and observes the lean-to-fat principle. A simple way of doing this is to start with a jar of Formula A.9 (containing not much more than that needed for the instrument), then add some Formula A varnish of the same colour to the jar after each coat is used. Adding about 5% (one part in 20) of Formula A per coat will do. A simpler way is to add about 3% of Stand Oil to what is left in the jar after each coat. Incidentally, adding a quarter of Stand Oil (technically 24% by weight or 26% by volume) converts A.5 Varnish to A.9 and A.9 Varnish to A1.4 (A) as we provide it.

VIOLATIONS OF THE LEAN-TO-FAT PRINCIPLE

It has been reported that a layer with high oil content (and subsequent low index of refraction) can reproduce the kind of glow or sheen claimed to be seen on Old Master instruments, and which is absent when such a layer is not used. The optical effect could result from multiple reflections in the oil layer of lower refractive index than its surroundings. Condax (CAS Newsletter 10, 1968) did chemical and physical tests on the first layer on top of the wood of Old Master instruments (which he called the "ground varnish") and suggested that it was dried linseed oil boiled in umber. Later, (CAS Newsletter 37, 1982) he suggested that the wood pores were filled with rosin oil, with a calcium caseinate protein "sealer" on top. A layer of oil would violate the lean-to-fat principle by having a thin fat layer in the wrong place. A protein layer would have the same effect because of low stiffness. If a layer of lower stiffness is keyed into surrounding layers by unevenness on a micro level or by including particles that are thicker than the layer thickness, the ill effects of violating the principle can be avoided. This could have been true sometimes and not others. It is possible that this is why the varnish on Old Master instruments seems to have been so inconsistent, often flaking off or crazing or wrinkling, and often not.

Nowadays, a method of putting colour onto the instrument called the 'glaze' method is quite popular because it makes the wood very attractive, though there is some loss in transparency. This method involves spreading artists' oil paints directly from the tube onto whatever filler/sealer one usually uses, and when dry, continuing with clear varnish. The artists' oil paints contain iron oxide pigment particles dispersed in linseed oil. The visual success of this method could be due purely to the linseed oil, in a way similar to that mentioned above. This method violates the lean-to-fat principle and could possibly lead to problems given enough time. The fact that these problems are the same as those with many Old Master instruments could be considered an asset if this actually was the method the Old Masters used. This is unlikely in general since, though particles of Madder Lake have been found, none of iron oxide pigment have been reported.

TREATMENT OF THE INSIDE

Many observers have remarked that there seems to be some transparent substance covering the original wood surface on the inside of Old Master instruments. It is likely that the purpose of this coating was to be a moisture barrier. The velocity of vibration propagation perpendicular to the grain can vary by as much as 10% with varying moisture content, so if the plates are tuned at one moisture content, they may well be no longer tuned when the instrument is played with a different moisture content. This is probably the main reason for variation in instrument quality with the weather and with seasons.

We have tested the moisture-barrier effectiveness of thin layers of many natural substances including varnishes waxes and oils, and found that polymerised linseed oil (Stand Oil) is by far the best.

COLOUR

NRI varnishes are available in oil ratios of 1.4 (Formula A) and 0.9 (Formula A.9). In addition, the clear varnish is available in oil ratio of 0.5 (Formula A.5). The colours are:

CLEAR: A slightly amber coloured clear varnish.

CHESTNUT BROWN: A reddish brown, the colour produced by heat with iron present.

WARM BROWN: A more yellow brown, produced by heat without iron present.

COLD BROWN: A brown with little or no redness in it, produced at a higher temperature.

MADDER RED: Redness is produced by a mordent of the active principle of madder root.

GREEN: The colour is copper rosinate, for reducing or eliminating redness in brown varnishes.

As one builds up thickness of the Chestnut Brown the colour goes from a golden brown, to a reddish brown, to very red when quite dark. The colour of the Warm Brown goes from a yellowish brown, to a medium brown with a tinge of red, to a dark reddish brown. The Cold Brown colour does not turn red as it gets thicker and darker. The colour of the Madder Red goes from a light orange to red with added thickness. As one looks through the varnish at different angles, the apparent thickness and therefore the colour varies. The Madder Red and Green varnishes have lower colour intensity than the brown varnishes. Mixing either of them with a brown varnish before application has rather less effect on the final colour than applying it (without mixing) in separate layers.

A particularly easy procedure is to apply brown coats until the desired darkness is reached and then add coats of Red to achieve the desired richness, or coats of Green to cool the colour. If one polishes clear varnish on top of the colour, it is surprising how pleasant a final thin coat of Red looks. Alternatively, one can use Red to build up the several layers for polishing. The salmon pink UV colour seen on Old Master instruments can be seen with a brown top coat, but not with a clear or Red top coat. The Old Master instruments apparently had no clear top coats on the colour coats and the surface was not polished smooth.

Curiously, when one uses fewer thick coats or more thin coats to get the same colour darkness with the same varnish, one gets a different shade of colour. There are differences again if one interleaves coats of different colours or if one dilutes the colour of each coat by the addition of clear varnish. In addition, we cannot guarantee to produce exactly the same hue of colour with each batch of varnish. Consequently, if one is trying to achieve a particular shade of colour, it is recommended that one experiments beforehand either on scraps of wood or onto pieces of glass (or clear rigid plastic) which one then places over the wood for evaluation.

COAT THICKNESS AND DILUTION

All NRI varnishes are very viscous, as the linseed oil is made into stand oil before mixing with the pine resin, and also because they contain very little added turpentine (about 10%). They may be thinned with turpentine or white spirit solvent. The only function of the solvent is as an aid to spreading the varnish, and it evaporates completely soon after application.

The colours of the brown varnishes are very intense. With the addition of our Varnish Levelling Additive, these varnishes can be used with a little thinning with solvent to make a thicker layer, or with more solvent for a thinner layer. A thicker layer can be spread by the hand (fingers or palm) or a lint-free cloth or a brush with a bit of stiffness. It is possible to get a coating as dark as those on the vast majority of Old Master violins with two such coats. Using a small number of thicker coats for getting to a desired darkness reduces the time available for dust pickup, besides getting the job done quicker. To aid drying, the use of our Hardener is recommended (one drop of hardener per 5 ml or teaspoon of varnish before any dilution with added solvent).

Using a larger number of thinner coats has the main advantage of making it easier to control the even spread of colour. Thinner coats dry faster, and if one worries about the hardener adversely affecting the varnish in 100 years (we don't think it will), there is a better chance that the varnish will dry within a reasonable amount of time using a minimum of hardener. A soft brush is appropriate for applying thinner coats with the varnish consistency considerably thinned with added solvent. A brush with sable or sable and nylon hair works well. Brush widths in common use are 3/4 inch for the violin, 1 inch for the viola and 1 1/2 inch for the cello.

If one finds that one cannot adequately control the evenness of colour with the colour intensity as provided (this is most likely to be the case if one prefers not to use the Varnish Levelling Additive), then one dilutes the colour intensity by mixing with clear varnish. The above considerations concerning thicker or thinner coats apply. If one is only varnishing to a fairly light level of colour, this practice will not necessarily lead to a total varnish layer which is unduly thick.

The colour induced in pine resin by heating (like NRI coloured varnishes) can fade in strong UV type B radiation. It is thus advisable to use UV A tubes in one's drying cabinet and not to dry coats in direct sunlight (which has both). UV B radiation, though more energetic than UVA, has little penetrating power, so the colour is much more durable in direct sunlight after the varnishing is finished than when each coat is directly exposed to it during the varnishing.

VARNISHING STRATEGY

There is evidence to suggest that the Old Masters purfled their instruments and did the final shaping of the arching in the region of the purfling after assembly. They would have then applied the ground mineral layer and varnish after this. All of these operations will affect the plate tuning, and so perfectly tuned plates before assembly may not remain so after varnishing. Some avoid this problem by purfling and varnishing before tuning and then revarnishing after assembly. Schelleng, from theoretical considerations, has suggested that putting a total of three times the number of coats on the back as one puts on the soundboard would maintain the same plate tuning relationship after as before varnishing. To accomplish this one could put a minimum on the soundboard, say ground (filler/sealer), colour coats and a top clear coat, and put three times the total number of coats on the back, with the difference being in clear coats on top of the colour. The thinning of the plate around the purfling could perhaps counteract the effect on the plate tuning of the added stiffness, particularly by the ground.

APPLICATION

When a coat of varnish is applied, every particle of dust on the surface underneath accumulates varnish around it, making the local thickness much greater than elsewhere. This is called a nib, and it needs to be removed, preferably as soon as it is apparent during application. Previously wiping the surface (which, if it is a varnish layer, must be quite dry) with a lint-free cloth impregnated with oil removes the dust particles and so reduces the incidence of nibs. Such cloths are called Tack Rags, and they are included in our catalogue of varnishing products.

After varnish is applied and spread over the surface with a brush, it is usually brushed repeatedly in one direction and 'layed off' in a perpendicular direction (laying off is brushing with the brush at a shallow angle to the surface). One stops (after laying off) when one feels a slight drag on the brush. If one stops earlier than this, the varnish can still flow away from the even distribution produced by the brushing and laying off. If one stops later, one will leave brush marks and patchy colour. If one stops at the right point, the brush marks will generally level out by themselves. One usually picks the laying-off direction to be along the main character feature of the wood (the grain on spruce and the flame on maple) so that any residual brush marks are least noticeable. If one gets streaks when laying-off, it may be time to get a new brush (one should not expect a brush to work well for much more than a half-dozen instruments unless one is scrupulous in its care). When one uses the hand or a cloth instead of a brush, the procedure is similar. There is also a stippling method, but we have no experience with it.

While the varnish coat is drying, if a hair or other debris falls onto it and gets stuck, one deals with it only after the varnish is quite tack-free (non-sticky to the touch) and firm, but not fully dry. With a rotary motion, one lightly rubs it with moistened (saliva is traditional) fingers or palm. This should dislodge the debris leaving the surface in acceptable condition.

If a coat is unsatisfactory, it can be removed after application and before drying with a rag dampened in solvent, providing the previous coat is thoroughly dry. If the preceding coat is not fully dried this procedure could have unsavoury results.

DRYING

The drying speed of the varnish will vary according to the conditions of light and heat as well as the thickness of the coat. The fastest drying will be in sunlight, but prolonged exposure to direct sunlight can lead to some fading of the colour. It is usually more convenient to use an ultraviolet (UV) drying cabinet, which contains one or more ultraviolet fluorescent tubes and is lined all over the inside with aluminium foil. This can easily be made oneself using standard fluorescent tube fittings and UV type A tubes. Both type A and the too-strong type B tubes are used for sun beds. We doubt whether humidity has any effect. Also, varnish varies somewhat from batch to batch. It is best to test a sample of varnish first under the proposed drying conditions, so far as these can be controlled.

To speed up drying, add about 10 drops of NRI Hardener per 50 ml of varnish. If drying is still too slow, add another 10 drops to 50 ml of varnish. We are not sure about how much more than this can be safely added. A single thick layer of Formula A varnish with 100 drops per 50 ml spread on both glass and metal remained in perfect condition after several years of thermal cycling in an accelerated-aging apparatus used by the paint industry. We believe that the cobalt in NRI Hardener prevents most of the problems resulting from using more than a small amount of a fully traditional type of hardener. That problem is that the surface can dry so quickly and thoroughly that it inhibits the diffusion of oxygen through it to dry the varnish underneath, which then can take many months to dry properly. During that time, a less flexible layer covers a more flexible layer, and the same problems can arise as with violation of the lean-to-fat principle.

We try to achieve drying conditions under which the varnish becomes tack-free in about 3 - 4 hours. Much longer than this increases the probability of dirt pickup. It will of course take much longer to harden fully. However, if the varnish has reached the tack-free state in the 3-4 hour period, it should be hard enough to accept another coat after one day. In all cases one should allow as much time as possible between coats, but as a rule-of-thumb one day is a practical minimum.

FINAL FINISHING

Some makers carefully polish the surface of the final colour coat and then add an untouched coat. Most polish on clear varnish, and some add an untouched coat. Before polishing, one should wait at least a half a week for the varnish to harden sufficiently. Then, remaining nibs can be removed with an abrasive such as 600 grit (or finer) wet-and-dry. If the final surface is to be polished, that is usually done with burnishing cream or special preparations for polishing plastics or car paint (such as T-Cut).

POSTAGE & PACKING

Each item has, for postage & packing purposes, a GROSS WEIGHT figure.

To work out your postage & packing prices, add the GROSS WEIGHTS of your ordered items together, and use one of the tables below.

The GROSS WEIGHT limit for any one parcel is 1500g.

NOTE: Due to postal regulations, the MAXIMUM amount of varnish allowed in one parcel is 1000g NET WEIGHT.

Therefore each full Kilogram (NET WEIGHT) of varnish must be posted and charged for as a separate package. Goods other than varnish may be included with lesser quantities of varnish up to the 1500g GROSS goods weight limit. Any remaining goods ordered over the 1500g GROSS goods weight limit or the 1000g NET weight limit is also posted and charged as a separate package.

If in doubt we will calculate your postage and packing costs for you and notify you of the total cost of your order so that you can arrange payment.

For small (up to 500 gm GROSS weight) parcels that do not contain varnish, please use the following table :

ZONE 1: North, Central and South America, Africa, Near East and the Indian Subcontinent

ZONE 2: Australia, New Zealand, Japan, China and the rest of the Far East

NOTE: The U.K. Post Office advises us to send parcels to some countries by 'International Signed For' as routine. This cost is added to relevant invoices.

WAYS TO PAY

We accept Visa and Mastercard credit and debit cards and Maestro and Solo debit cards. The 5% prepayment discount. does not apply. For security, the card information should be given to us by phone, fax or post.

We can accept cheques, money orders or bank drafts only if they are in £ (pounds) Sterling that go through a U.K. bank.

Payment can also be made directly to our NRI account at the HSBC bank at 577 Wilbraham Rd., Chorlton-cum-Hardy, Manchester M21 1AH, U.K.; Sort code: 40-31-17; Swift code MIDLGB22; BIC: MIDLGB2144P; IBAN: GB34MIDL40311781389955.

Northern Renaissance Instruments

6 Needham Avenue, Chorlton-cum-Hardy, Manchester M21 8AA, U.K.

Phone & Fax: +44 (0) 161 881 8134 ; proprietor: Dr. Ephraim Segerman [USA]

e-mail: post@nrinst.co.uk ; on internet: http://www.nrinst.co.uk

VARNISH ORDER FORM