Brown Varnish formula, slightly modified from Kettenburg’s formula published in Muzzleblasts (
http://www.muzzleblasts.com/archives/vol5no2/articles/mbo52-1.shtml).
½ pint linseed oil
2 oz gum benzoin
2 oz rosin
1 teaspoon lead carbonate
Add lead carbonate to cold linseed oil. Heat to 400
o – 450
o (F) for 30 to 45 minutes, then allow to cool. This is now boiled linseed oil (BLO). If you don’t have a high temperature thermometer, one period recipe calls for heating the oil until it will scorch a feather. This works very well. Feathers scorch at about 460
o F according to my thermometer.
To make a varnish, you need to add resin to the BLO. Grind the rosin and gum benzoin with a mortar and pestle, or marble rolling pin. The resins should be as fine as flour.
Dissolve rosin in 1/4 – 1/2 pint of turpentine by vigorous shaking in a glass jar for a couple of minutes. Add immediately to cold BLO.
Dissolve gum benzoin in ethyl alcohol (denatured alcohol or moonshine) and add immediately to cold BLO. Not all of the gum benzoin will dissolve, but get as much in solution as you can. Heat BLO/resin solution slowly with constant stirring to 225
o-250
o (F) for 10 - 15 minutes. There will be some non-soluble black goo from the gum benzoin, but slow heating and constant stirring will minimize goo formation. Do not filter the resins before adding to the BLO.
There are a lot of caveats and much to talk about in the production of varnish. Here are a few:
1. You do not have to dissolve the resins before adding them to the BLO. I just like to do it that way because I think everything goes into solution easier. If you want to add the resins without dissolving them first, I’d add the resins to warm oil.
2. The turpentine is a required ingredient, the alcohol is not. The alcohol boils off so it isn’t part of the final varnish.
3. Gum benzoin is not completely soluble. There will be more or less black tarry stuff left in the bottom of your pot that you will never get completely out. My wife does not have a sense of humor that encompasses making varnish in one of her pots.
4. An electric heat source such as an electric burner or electric frying pan is highly recommended. If you’re a sporting type, go ahead and use an open flame. Your whiskers will probably grow back. Some day. Mine did anyway.
5. The times and temperatures are not too critical, except for two points. You will see bubbles start to form around 320
o. I suspect this is where the name “boiled” oil comes from – it looks a lot like boiling water. The bubbles though, are carbon dioxide from the lead carbonate, and indicate that the lead is going into solution and combining with the linseed oil. This is the minimum temperature you need.
The other interesting temperature is 649
o, which is the auto ignition temperature of linseed oil. You don’t need a thermometer to tell you when you have gotten to this temperature. Same comment about whiskers.
6. So, between 320
o and 649
o, longer times and/or higher temperatures make thicker, darker, faster drying oils. You don’t need a thermometer to keep you in the correct range – a few feathers will do the trick. As far as time goes, about 20 minutes above 320
o seems to be the minimum to get all of the lead into solution.
7. Ingredients matter.
For gum benzoin (also known as gum Benjamin), get the raw resin or tears as they are also called, from Sumatra. Not processed resin, not tincture of gum benzoin. It is supplied in a really raw form, full of bark, sticks and dirt. Fish out the big chunks of wood and don’t worry about the dirt. There is no way for us to get it out now, and there was no way to get it out in 1750 either. People who have looked at original finishes under a microscope say that they are easy to tell from modern finishes, because of the amount of dirt in them. Don’t worry about it – it is not apparent in the gun finish.
There are many grades and types of linseed oil, most of which are not suitable for gun varnish. Use either Varnish Makers Linseed Oil or Swedish Cold Pressed Linseed Oil. Here’s a source:
http://www.woodfinishingenterprises.com/coating.htmlAlternatively, you can use raw linseed oil (cold pressed only), but that needs some processing. Put the raw oil and an equal amount of water in a jug and shake it hard for a long time, then put it in the freezer. The water dissolves the water soluble components in the oil, which you don’t want in your varnish. In the freezer, the oil and water separate, and the water freezes so you can remove it along with the dissolved impurities. Do this a couple of times and you will have probably the same oil they used in the Way Back Times.
Most other types of linseed oil have been chemically abused and are not suitable for varnishes.
You can buy pure rosin from a chemical supply house, or you can go out in the woods and collect your own. According to one luthier who is very knowledgeable on the topic, raw natural resin, dirt and all, makes superior varnish.
Turpentine matters too. Oxidized turpentine is best. You can buy this from an art supply store, or make your own. To make it, bubble oxygen through the turpentine, or just leave the lid off for a couple of months.
8. This varnish dries with a high gloss. The correct way to cut back the gloss is to have your apprentice make some brick dust, then have him rub the stock with the dust and a little bit of linseed oil until the desired finish is achieved. Be sure he does a nice job.
If you research brown varnish, you will also see it in period literature as “common varnish”. Brown varnish was considered suitable for outdoor exposure, and one source I read noted that it would withstand boiling water. This is important because now you don’t have to worry about your gun finish in case you fall into a boiling hot spring, or use the butt of your gun for stirring the camp cooking pot. Try that with a modern plastic finish…
9. The finished product is essentially lead paint, without any pigment. So, a disclaimer:
WARNING: Lead known to the State of California to cause cancer. I don’t know if it causes cancer in other states, but I suppose it might.
This is the stuff that comes to mind immediately, but there is much more to talk about. If anyone is interested in discussing the chemistry, I can talk with you about the basics, but even better, the Mad Monk is around.
