There are two ways to get hold of shellac. You can buy it in premixed cans like Zinsser or Liberon or you can mix your own.
Making shellac is a simple process whereby we dissolve flakes of shellac we buy in crunchy flake form into 190 proof denatured alcohol, which we either buy through license here in the UK or we use Methylated spirits, which is denatured alcohol with an added violet colouring and any of a number of other additives that make the Meths undrinkable and even poisonous to prevent the misuse of it as an alternative cheap intoxicant. Methylated spirits and Denatured Alcohol are basically one and the same – Ethanol, which is used universally as an industrial solvent for creating products used in finishing, dyes and more and also for making and thinning finishes like shellac. The main additive used in Methylated Spirits is Methanol, hence the name Methylated Sprits. Adding methanol to denatured alcohol doesn’t alter the chemical properties of the alcohol apparently.
I use a glass jar or a plastic bottle to mix my shellac in, but it has a fairly short shelf life so mix only what you will use within a few months; no more than six, I would say. Whatever you mix, make sure there is enough room for the shellac flakes plus some for agitation during dissolution.
Denatured alcohol in any form and with any additive that makes it Methylated spirits is highly inflammable. Never try heating it on or near an open or even indirect flame.
You can buy shellac made ready for dissolving in different forms such as pearls, flakes or pre-crushed flakes. The shellac can be in different forms depending on what you want. In its natural condition, shellac is a dark amber coloured. Sometimes we want the dark amber and other times, in my case most of the time, we want the shellac bleached and dewaxed. That being so, we buy bleached and dewaxed shellac which simply means what it says. The shellac is less waxy and can be colourless or clear. French polishers use both the natural colour of the shellac and blond or clear and then also degrees of colour for their work and this is usually governed by the colour of the wood they are polishing. Light woods such as maple or cherry will turn amber with full coloured shellac flakes. If you do not want this as a colour you must use bleached shellac.
Add the shellac flakes or pearls into the liquid and shake regularly to agitate the mixture, which speeds up the dissolution process exponentially. Leave it stand long enough between shakes, about half an hour or so usually. Depending on the conditions of the shellac manufacture, the shellac may need straining through cloth to remove contaminants.
You can make different cuts to suit your needs. I generally use premixed shellac for everyday work, but there is no doubt that home mixed shellac is indeed best. Whether you make your own or buy it ready mixed, shellac can be thick or thin and this depends on the ratio of denatured alcohol to the pound weight of shellac used. Hence we use the term ‘cut’ because when we mix shellac with the solvent we create different viscosities to work the shellac at different stages in our work. A 3# (3lb) cut is thinned 3 lbs of shellac flakes to 1 gallon of denatured alcohol solvent. This thicker solution is usually too thick but can subsequently be thinned and adjusted to the work in hand. A more general cut is a 1# cut. I find it satisfactory to make a heavier mix and thin down as needed but a 1# cut is good for padding on and a 2# cut is good for brushing on.
Remember to use dewaxed shellac as a primer coat painted finishes as the paint will not adhere well to waxy shellac.
Pound cuts seems a little archaic when most of the world uses a metric system of weights and measures and perhaps we should simply go by quantity ratios of liquid to weight or measure quantity by volume. It’s not a critical thing in fact it’s fairly open to do that. Here in the UK we generally mix 250g of shellac flakes to a liter of Methylated spirits. You then add additional more flakes or meths to thicken or thin the viscosity to suit the task. My usual is to mix a heavier mix and thin. That way you have no down time waiting for shellac flakes to dissolve.
Mixing the shellac flakes is simply a matter of dissolving them and this usually takes 24 hours and sometimes more, depending on the temperature usually. If it’s too cold it takes longer and you can use warm water baths to increase the temperature or other heat sources such as radiators. Remember, no open flames of any kind or hot plates. This stuff is flammable. You can stir the flakes or shake them in the solution periodically. I shake them generally and then let it stand to express air in the mix before I use it. I usually shake whenever I remember, but generally every half hour works well. This will halve the dissolution time.
Don’t get too caught up in the thickness of the shellac too much. You can always readily thicken or thin your product and you can always use whatever you mix. If it’s too thick it’s more difficult to use that’s all.