Dec 072016

When it comes to finishing stocks for antique guns I like to use the traditional materials – partly for authenticity and because they are pleasant to work with, although undoubtedly not as durable as a thick coat of polyurethane varnish!   Guns were finished using one of two methods, oil finishes or spirit varnishes.  Oil finishes basically use mixtures of oils (usually boiled linseed oil) and waxes ( beeswax and other hard natural waxes) and harden by the oxidation of the oils by oxygen in the air, which takes place fairly slowly – driers, typically based on manganese compounds, are used in low concentrations to speed up the oxidation. The alternative traditional finish was spirit varnish, using a solvent – typically alcohol, in which a naturally occurring material that is transparent and hard is dissolved – typically shellac (secreted by an insect) or occasionally copal varnish (from the resin of a tree), or other resinous material – alcohol and Shellac are the ingredients of traditional French Polish and were very widely used before modern synthetic materials displaced them.   Spirit varnish hardens by evaporation of the spirit  to leave a thin coating of the varnish – the alcohol evaporates rapidly so the varnish hardens quite quickly and far fewer coats are needed compared to oil finishes, but its more difficult to get an even finish. Shellac varnish itself has a brown tint, and so does darken the wood slightly – the better the quality of the shellac the lighter the colour.    It is also possible to use both materials on the same job.


Potassium Permanganate:  Traditionally wood was either used in its natural colour or stained overall with Potassium Permanganate dissolved in water , a strong purple colour that dyes wood a natural looking brown colour – it was very widely used in Victorian times before spirit varnish on mahogany furniture.   It is a good way to colour light walnut to a darker tone.    (Potassium Permanganate was used as an antiseptic in times gone by as its a strong oxidising agent).

Van Dyke Crystals: This is a natural  water soluble dye derived from the husks of walnuts, that gives a good warm  brown not dissimilar to the colour of walnut wood, which is not really surprising given its origin.   I use Potassium permanganate or Van Dyke crystals diluted in water quite sparingly, and if I only want a light colouring on new wood I damp the wood slightly with plain water before using the dye to limit the amount that soaks in. It’s much better to use a number of pale coats to achieve the desired depth of colour than to try to get it in one go – its a pain to have to sand off an unwanted depth of colour!  Van Dyke dissolved in water is a good stain for touching in  repairs, but won’t work after oil has been applied.  Do remember when colouring that the oil finish, and to a lesser extend the spirit finish, darken the wood  and bring the grain to life.

Alkanet / Red Oil :  Another way of slightly deepening the colour of stocks etc. was by using oil that had been left in contact with Alkanet root  (Alkanet is a herb of the Borage family).   The red dye in Alkanet is not soluble in water  but is soluble in linseed oil, so a jar 1/4 filled with loose Alkanet root chippings and topped up with linseed oil can be left in a warm place for at least  few days or weeks and the oil will acquire a nice red colour – I leave the oil on the Alkonet.  Typically this was used for the first few coats – I use the red oil diluted with pure turpentine and with one or two percent of driers for the first couple of coats on the bare wood so that it soaks in well.

Talc:  I use talc (as in talcum powder) as an initial grain filler.  Talc (a clay mineral – hydrated magnesium silicate) is available as baby powder, but look for pure talc without additives or perfume!  It has the property that its a very fine, soft powder that is in fact more or less translucent when in an oil or varnish, so when used as a grain filler it doesn’t make the wood look ‘cloudy’ or ‘muddy’, and it comes in a very fine powder form.

Wood Dyes:  Wood dyes come in two sorts, water soluble dyes and spirit dyes.  In my experience the water based dyes are not true dyes but are pigments and leave the wood looking a bit ‘muddy’, so I avoid them.   I have a set of little bottles of various shades of   spirit dye that I use with a small artists paintbrush to match in small bits of wood that I have inlet.  I usually use the spirit dyes after I have started the finishing process, so that they don’t soak into the wood and colour it too deeply – they will be ‘picked up’ by the initial layers of oil finish and colour it very slightly, which gives you a chance to make progressive changes until you get the match you want.     I very occasionally use a black marker pen to darken down bits – again I wouldn’t use it until I had started the oil finish, and, as with the spirit dyes, I usually wipe it off fairly quickly with a finger to soften the edges.  One problem of using spirit dyes on top of oil is that the liquid migrates to the edge of the area and leaves a sharp line if you don’t wipe it off to blend it in.

Linseed oil:    This is the basic traditional stock oil finish used in the gun trade, and the basis for traditional oil paints.  It comes from the seeds of the linum plant – from which flax is also derived.  Linseed oil is available in several forms, but most commonly as either ‘boiled linseed oil’ or ‘raw linseed oil’, but occasionally as ‘twice boiled’.  Boiling it enhances its gelling and hardening properties, but some users say that there isn’t much difference and that  ‘boiled Linseed oil’ is often just the raw oil with driers added.  I use boiled for stock finishes, but to rub off a gelled oil finish I often use raw linseed.   WARNING:  if cloths and tissues are allowed to dry out with linseed oil on them they may spontaneously burst into flames and set fire to your workshop/house.  It is particularly dangerous if you use fine steel wool with the oil, as steel wool burns vigorously and gives off a lot of heat. Dispose of used cloths etc safely or leave outside, or do as I do, put them in the woodburning stove.

Terbene Driers:  Traditional accelerator for use when painting with oil paints in cold conditions to speed up drying, its a purple liquid based on Manganese compounds that helps with the oxidation process of the oil.  It is used in concentrations of one or two percent – too much and the oil film may go too hard and brittle, or so they say!

Slackum:   Slackum is the name given by old gunsmiths to the traditional finish they used – there is no hard and fast recipe but the recipe I use varies with each batch without materially affecting teh result.  A typical recipe would be  100 parts by weight boiled linseed oil,  5 to 10 parts by weight of grated beeswax and 1.5 parts of Terbene driers.   Stand it in a water bath and heat the bath until teh wax has disolved.   If you want more colour, use Red Oil in place of some or all of the linseed oil.

Grain Filler:  My grain filler is made by mixing talc with slakum to make a slurry that can be rubbed across the grain to fill the pores in the wood.

Rottenstone:  Rottenstone is a very finely divided mineral that is a darkish brown colour.  It can be used on a dry cloth to give a very fine polish to the oil finish, and at the same time will fill  the grain. Subsequent coats of Slackum  will incorperate the Rottenstone into teh finish

Preparing the work:   This is the tedious bit and the most important bit too – if you don’t get the wood  smooth and scratch free, no amount of oil or spirit varnish is going to produce a good finish.   You do need to work down through the grades of good quality paper – there are lots of modern abrasive papers that work really well – lubricated papers are excellent – and there is no excuse for NOT following the grades as far as 600, ( e.g 240,320,400…) after which I would probably use 0000 (the finest grade) steel wool.   The other important job is dealing with the grain of the wood – sanding is not a very good way of finishing wood, on fine furniture one would use a scraper, but sanding is the only way to deal with complex curved surfaces so we are stuck with it.  Even if you sand in both directions across and with the grain you leave a lot of fibres that are partly free of the surface and are liable to stand up when you apply a finish and spoil the surface.  To deal with this you need to make them stand up and then sand them off, and then repeat a couple more times. They can be made to stand up by damping the surface all over evenly but not soaking it, or my gently steaming it a – in either case let it dry completely before the next stage of sanding.

WARNING:   I should issue a warning at this stage – I use my fingers and hands a lot in stock finishing because feeling the wood tells you more than the eye about the shape and texture – I also apply oil with my fingers and rub it in with my hands in the traditional way – this is not really a good idea – the health and safety people say you shouldn’t get linseed oil on your skin so YOU should try wearing tight fitting  latex gloves – my justification is that I’m too old for it to make any difference now.

First thing to take into account is that every piece of wood is different, and so will respond differently to any given treatment – getting a good finish depends on adapting your work to suit the situation.  Unfortunately the cheaper the wood the more open the grain and the more trouble it is to get a good finish.  If we all started with figured walnut from the bole of the tree it would be relatively easy to get a reasonable finish, but if the wood has a fairly open grain you will have more work to get it a comparable finish.

My finishing  would normally proceed in the following stages;

  1. Sand as above until you are sure that there are no scratches of marks
  2. Raise grain and sand – repeat a few times until the surface is smooth.
  3. Apply stain as required but don’t aim for the shade you want in one go – keep it on the light side.
  4. Dilute Red Oil  with 25% Turpentine and apply liberally – leave in a warm place – repeat a couple of times wiping off any runs etc and trying to keep it evenly coated.    Some stockers immerse the whole stock in hot oil for a few hours.  You should now have got an idea of the colour that your finished stock might be.
  5. Rub a coat of the grain filler across the grain and lightly wipe off any surplus. Leave for a few hours in a warm place and polish off any remaining slackum with a cloth – if necessary damp the cloth with raw linseed oil. You might need to do several grain filling coats but don’t be afraid to leave some grain visible unless you are aiming for a ‘Purdey’ finish!
  6. The basic repeated process for building up the oil finish is to apply slackum generously with a finger and leave it to gel.  When it is well gelled, but definitely before it begins to go hard you need to rub it ff with a cloth damped with raw linseed oil and finally polish off lightly with a tissue.  A few goes will tell you how long it takes to ‘go off’, probably between 4 hours and 12 hours, but don’t leave it to go hard – if you don’t know that you are going to be around when its due to be rubbed off, just take off all the excess slackum and leave it until you have a window to do a proper gelled coat.  It doesn’t hurt to leave the finish for a few days between coats.  If you do leave a thick coat of slackum too long and it sets so that you can’t rub it off, you’ll have to take it off with 0000 steel wool, which effectively means starting over again- so don’t!
  7. As the finish builds up you may want to rub it down lightly with rottenstone so as to fill up any remaining grain – run gently across the grain- and polish off any surplus before applying more coats of slackum.  When you have reached an endpoint just polish off the oil finish and leave it for a week or two to fully harden.  You might find that you need between about 10 and 40 coats to get it to the stage you need.
  8. Polish gently with a soft duster and stand back and admire!

  2 Responses to “Wood Finishing”

  1. I tried your slalom one a set of Pau Rosa cleaning rods I made for a doglock fowling piece as the gain is very closed I did not think I needed any grain filler. I found that the slakum did not dry for several days and after many coats it was not filling the tiny grain pores despite even adding another dollop of driers. So I decided to have a go with the talk grain filling slurry. Surprisingly the following coats of slakum dried very rapidly. I wonder if the talcum powder acts as a catalyst in the polymerisation process?

    • Hi Howard,
      Not sure I can throw much light on the problem! I think there is a general issue about what is sold as ‘boiled linseed oil’ – some of it just has a bit of driers added, or so I’m told. I am not sure why the talc would accelerate drying – the talk I use is BP, i.e. pure medical grade. Talc as purchased may have other ingredients that have a drying effect – I guess if it contained any metalic elements in any form it might do that – possibly aluminium as an anti perspirant?

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