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"How To" Use Shellac
Cap the container and allow it to dissolve 24-48 Hrs before using
How to use Shellac for pore filling.

Wood is made from Grain and Lignin (binder like glue), anything we put onto the surface soaks into the lower layers, so using shellac we can seal the upper layer
Using a cotton cloth dipped into the shellac, rub it into the surface and allow 2 hrs of drying time
Here we have a piece of Mahogany taped down the centre, one side we will shellac the other side we will leave alone

There are numerous sources from people far smarter than I, on what shellac is, so if this information wets your appetite, search google for more.

For simplified version, shellac comes from a female lac bug, when she feeds on the sap of the tree, she excretes sticklac onto the bark surface behind her.

In lutherie, we generally use blonde shellac for sealing the wood and or providing a finish.

Blonde shellac is not referring to the colour, it's referring to the process it's been put through after it has been scraped from the bark, the process removes the wax component of the mix so that way it does not react with paints and finishes.

We refer to the mix of shellac and alcohol as a cut. Example a 2 pound cut means we have two pounds of shellac mixed with one gallon of alcohol. A 3 pound cut is 3 pounds of shellac to one gallon of alcohol and so forth.

The colour of the natural shellac comes from the type of tree the lac bug is feeding of. Post processing can change the colours via bleaching and stains, you can also purchase shellac in flake or solid forms.

Shellac is thinned for use in lutherie by mixing it with denatured alcohol (methylated spirits), this turns it into a liquid solution, as the alcohol evaporates, it reverts back to a more solid form.

Once mixed it has a shelf life of around a year, to test if liquid shellac is good, we drop a little onto a glass surface and see if it evaporates, if the end result is a hard piece of shellac then the mix is good, if the end result is a tacky piece of shellac, the mix needs to be disposed off.

For lutherie i prefer using a 2 pound cut, We mix this in small ratios 30 grams of shellac to 120 mls of Methylated spirits.
Mix, we now have a 2 pound cut of shellac.
Lightly scuff the surface with 400 grit sandpaper to remove any high fibres
Rub another coat onto the surface and allow a further 2 hrs drying time
Using a glass of water as an example, we pour it over the surface.

You can see the untreated areas of wood, soaking the water in, the shellac'd wood has been sealed and protected and has no uptake of the water, it beads on the surface