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Mixing Shellac
 
Mixing Shellac
Created by Steve on 8/29/2010 7:43:28 PM

Mixing shellac fresh from flakes is no more difficult than dissolving sugar in a cup of hot coffee.  Granted, it takes longer for shellac to dissolve; but, the skill set is the same...we are simply dissolving a solid in its solvent.



Shellac

Mixing shellac fresh from flakes is no more difficult than dissolving sugar in a cup of hot coffee. Granted, the process takes longer since shellac does not dissolve as quickly as sugar.  But, the process is precisely the same. A sold is placed in a liquid solvent where it dissolves, quite on its own with no action required on the part of the user other than the initial combination of shellac and alcohol. So, why is there so much resistance? Why is it that the simple process of putting a bit of dry shellac in a container of denatured alcohol is viewed with so much trepidation? Why do so many insist on buying pre-mixed shellac, with all of its disadvantages, rather than opting for the easy, and ultimately more economical path of mixing their own?

I can't answer these rhetorical questions. I can only surmise that it is fear of the unknown. Fear, or reliance on myths that persist in spite of the fact that they are so easily refuted. Yes, shellac can be purchased pre-mixed from a number of sources including your local paint & hardware store, or any of the "big-box" chains.  But, shellac purchased in this form lacks the quality and flexibility of shellac purchased in dry form and mixed fresh as needed. Pre-mixed shellac is fine for rough applications such as sealing knots in lumber that you intend to paint or "sealing" pet stains on plaster and drywall.  However, for most other applications pre-mixed shellac simply lacks the flexibility that finishers (should) expect.  Most of the stuff contains wax, its "grade" is often inconsistent, to say nothing of inappropriate in most applications; and worst of all, it has already begun to degrade by the time you take it home—shellac, as you will see later in this article, has a finite shelf-life once it is mixed.

So, while pre-mixed shellac can be a quick and easy answer to some finishing questions, if you intend to venture into the wonderful world of shellac as the finish (or part of your finishing schedule) for fine furniture and cabinetry, you should purchased your shellac dry and mix your own. Mix it fresh, as needed.

Shellac is mixed according to its "Cut". Cut defines the the amount of shellac by weight that is mixed in a gallon of alcohol. For example, one-pound (16-ounces by weight) of shellac dissolved in one-gallon (128-ounces by volume) of alcohol is a 1# cut. Two-pounds (32-ounces) of shellac dissolved in the same gallon of alcohol produces a 2# cut. The heavier the cut the greater the amount of shellac resin ("solids") in the mix. The relationship between ounces of shellac by weight and ounces of alcohol by volume is important since it would rarely be desirable to mix a full gallon of shellac. Once mixed, shellac begins to degrade. As a rule of thumb, after 6-months the shellac will no longer dry properly. So, with that in mind, it is important to mix no more shellac than you plan to use on the project at hand. Shellac flakes, on the other hand, will last indefinitely if kept cool and dry. I keep my shellac flakes in a refrigerator.

The following table shows the amount of shellac by weight (column below # cut) that one must mix with a given volume of alcohol (left column) to produce various quantities of shellac mixed in different cuts.


 
# Cut
   Alc
1#
2#
3#
4#

V
o
l
u
m
e

4
.5
1
1.5
2
8
1
2
3
4
16
2
4
6
8
32
4
8
12
16
64
8
16
24
32
128
16
32
48
64

The dilution of shellac from one cut to another can be a brainteaser that will have you sitting in a corner talking to yourself.  I find that many of the "simple" conversion methods solve only half of the problem.  When converting from a heavy cut to a light cut not only do I want to get the cut right, but I also want to be able to mix a specific volume of shellac.  For example, if I need 8 ounces of 1# cut how much of my 3# cut do I need to thin, and by how much, in order to reach my goal.  If I use a simple ratio I risk winding up with too little or too much.  I need a way to get both the desired cut and the necessary volume.  In this way I don't waste shellac; or worse, have a collection of partially filed containers sitting around, each holding a small amount of shellac mixed to a different cut, and all slowly going bad.  Here is how I calculate dilutions:

A 3# cut is 48 ounces of shellac (by weight) dissolved in 1 gallon (128 ounces by volume) of alcohol.  A 1# cut is 16 ounces of shellac dissolved in one gallon.  16 ounces divided by 48 ounces is 0.33. That is the same as saying that a 1# cut is 33% as "heavy" as a 3# cut. Therefore, if I want 8 ounces of 1# cut shellac I multiply 8 times 0.33 to determine how much 3# cut must be contained in my new 8 ounce volume of 1# cut. The result is 2.67 ounces.  Therefore, if I put 2 2/3 ounces of  3# cut in a measuring cup and then fill the cup to the 8 ounce mark with denatured alcohol I will not only have the desired cut, but I will also have the exact volume that I need with no guessing, no confusing ratios, and no waste.

Here is the simple formula for the dilution I just described:

  • (Weight of shellac in Target Cut ÷ Weight of shellac in Stock Cut) x Ounces Needed = Volume of Stock Cut
  • Top-off to desired volume with denatured alcohol.

Example:

(16 ÷ 48) x 8 = 2.67 Ounces of 3# Cut topped off to 8 ounces will yield 8-ounces of 1# cut.

 

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