Slacum
Now to the fun- and labour intensive part of a Slacum finish.
I will not go into my process of preparing the wood more than that I use the same method as Purdey with wet sanding and going to from coarse smaller grain size. I usually end up with 2000 grit. I have now obtained some rotten stone and will try this together with a “chammy” cloth for burnishing. I have tried 0000 steel wool but I found I to be coarser than 2000 grit (visible through a magnifying glass) and it also leaves residue in shape of small metal particles which are almost impossible to get of the wood and that will reappear in the finish as flakes…that seriously ruins Your day.
As for my self I use the sensation of “feel” to check when I am through with sanding and burnishing. When You cant actually feel the wood surface although You are running your fingers over the surface You are getting there. The sensation is almost a bit eerie. You can se Your fingers running across the wood but You cant really feel the wood.
For me the purpose of a oil finish is dual- protecting the wood against moist and giving it pleasant looks.
Then there is the magic concoction of the Slacum…. For my self I have used a bit of everything from pure boiled linseed oil and raw linseed oil- these to mixed in different proportions and added balsamic turpentine. Do not ask me for measurements since I only mixed these by feel (no heating involved) and I have no clue what so ever what’s in my bottles right now. I have used these mixtures both for grain filling and penetration and used the CCL Gunstock conditioning oil for the end finish. I do not use any grain filler more than sanding in dust in the pores when sanding. I have not yet put any “filler” into my Slacums.
Well time to get a bit more methodical in my approach and I found the to recipes from Dig and Salopian which I shortly recite below.
Dig´s
Boiled linseed oil 16 oz
Spirits of turpentine 2 oz
Carnauba wax 200 gr
Venice turpentine - 2 teaspoonfuls
Salopian
1/2 pint of Raw Linseed Oil
2 ozs of Plaster of Paris (Dental Quality)
1/2 fluid oz of Butter of antimony
1/2 Gill Spirits of Wine
2 teaspoons of Vinegar
1 teaspoon of Venice Turps.
Salopian on Manton
Cold drawn linseed oil 1 quart
Gum Arabic (dissolved in warm water) 1/2 ounce
Alkanet root 2 ounces
Rose pink 1/2 ounce
Vinegar 1/2 pint
Boil these together and then let stand for 1 or 2 days.
For starters we can se that the recopies are quite alike in quite a few parts, but they also differ. I don’t say that one of them are more “correct” than the other- there is many ways to skin the proverbial cat..
The “oily-part” is covered above so I will focus mainly on the additives and their function in the Slacum.
There are a couple of the additives that reoccur in the slacums (oil excluded) and that is balsamic turpentine and Venetian turpentine.
What do these contribute with to the Slacum?
To my understanding the balsamic turpentine have to effects. It lovers the viscosity of the Slacum- hence supporting the penetration and pushing the oil deeper into the wood, BUT I also understand when it evaporates it can push the oil out towards the surface again which should be counterproductive? Any comments on this thesis?
I have also read that the balsamic turpentine aids the Drying/hardening/polymerization, but I have not seen any good explanation to this “chemistry”. Does anyone have a bit deeper information regarding this.
Venetian turpentine. For me a mystery so far. Got a bottle the other day from an art store. Thick and smells a bit less then regular turp. Expensive to say the least….
Aids the Drying/hardening/polymerization process? A substitute for Gum Arabic as in Manton’s recipe?
Gill spirits? Lovers the viscosity? Aids the Drying/hardening/polymerization process?
Vinegar? Aids the Drying/hardening/polymerization process?
Butter of antimony? Yet another mystery. Aids the Drying/hardening/polymerization process?
And as a last note for now.. Have You experienced that your Slacums deteriorate over time if exposed to sunlight and air? I have found that some of my mixtures have clogged up when left in a bottle for a year or so. When that happens I usually put some balsamic turpentine in the mix to dilute it. Sometimes it works and sometimes it doesn’t.
If You have managed to plough through this ordeal of information I am more than grateful and I hope there will be some interesting debate-once again- over this fascinating subject!
I wish You all a Merry Christmas and a happy new Year!
Best Regards Erland
