If you have the privilege of owning a home that was built between the 1920's and 1960's, and your woodwork/cabinets have an yellow/orangish color color to them, then more than likely they have shellac on them.
Shellac, in its natural form, is a by-product/resin from a forest bug in India and Thailand. The flakes of the natural resin can be a number of colors - pale yellow, orange, dark orange, or almost burgundy. The flakes are harvested and sold as a dry good for numerous applications and uses. Typically the flakes are dissolved in an ethanol or denatured alcohol solution in order to give it a liquid consistency. The rate at which the solvent was added to the dried flakes was referred to as 'the cut rate'.
If you look at the time period in which this product was immensely popular, you will notice that it directly correlated with many men coming back from WWI & WWII. The housing boom, in some areas, that took place when men returned from the front was almost unquenchable. I remember hearing stories from 'old timers' that said rail cars couldn't deliver enough lumber for all the construction that was going on. It was time to build because families were being started.
How does this exactly relate to painting, you may ask? Well, shellac was used as an all-in-one stain and finish product on a lot of trim woodwork within the previously stated time frame. This product allowed painters & carpenters to save time because it was an all-in-one product, it would dry quickly for a re-coat, was durable, and was readily available. The product was used to save time which is vital when you are confronted with many houses that need finished in a short amount of time.
Shellac has fallen a little out of style due to the advancement of other products such as lacquers, nitrocellulose lacquers, varnishes, polyurethanes, and others. But some of the qualities of shellacs are still applicable. Shellac based primers are an excellent choice for sealing in smoke damage, odors, and stains. Shellac products can also be used as a universal sanding sealer or finish on woodwork.
I try to keep a quart of amber shellac, denatured alcohol, and shellac sanding sealer handy because of the universal application. Just know that you will have to clean up tools/brushes with denatured alcohol. If used in a large area make sure that there is adequate ventilation and proper respiratory gear is worn. You also may have to reduce the shellac with denatured alcohol in a separate container in order to make it easier to apply(so it doesn't dry too quickly for you) and more user friendly. Please refer to manufacturer's recommendations on the side of the can for the proper cut rate of solvent to the liquified shellac. If I see that some trim work, in an older house, needs a fresh look - shellac is the go-to product.