Decode Your Shellac

I use shellac on nearly every project that passes through my shop doors. I think it is the best product for furniture because it is easy to use, can be brushed on or sprayed, and  dries quickly compared to urethane. I use shellac on top of aniline dye and even on top of a coat of boiled linseed oil if I aim to highlight figured grain. It is my “go to” finish before and after glaze. As you can tell, shellac is, in my opinion, the perfect topcoat. I’m good with shop-made shellac from flakes and I use store-bought shellac from Zinsser.

Until recently, my only problem with shellac – all shellac – is that I do not care for the high sheen that comes when shellac is built-up as a finish, but I have found a great work-around. I apply a coat of dull-rubbed effect lacquer, or I rub-out the surface using #0000 steel wool or an equivalent. Over the last year or so, I have developed a second problem with Zinsser shellac purchased from hardware stores or the large home-center stores.

As you undoubtedly know, shellac has a shelf-life. From the moment it is mixed into solution, it begins to degrade – degradation effects drying times. Eventually, as the degradation continues, you end up with a gummy mess with which to deal. Experience taught me this lesson, so I watch my dates closely.

A while back, Zinsser switched from using a date stamp on can lids to a lot number. With the date stamp, and the fact that the company-issued literature states its shellac was good for three years after the stamped date, you had a good idea as to when the shellac would reach it’s end. Even today I can go into a local home-center store and find shellac in gallon cans with a date stamp of 2008 – in 2012, that can is not one I’ll purchase.

With a lot number, there was no way to tell when the shellac was mixed. Or so I thought. I contacted the company, explained my dilemma and was pleasantly surprised when I received a reply that same afternoon. I now know how to read the lot number to tell when the shellac was mixed. Here is the information.

The first number after the letter is the year the shellac was made. If you look at the number in the photo, you see a zero. That shows the year at 2010. The number one would represent 2011 and a two is for 2012. Easy enough. That’s probably all the information you need, but the company goes further.

The first number after the year indicator stands for the month of mixture. In this case there is a seven, so this can of shellac was mixed in July. If the month would have been November you would see an “N”, December is a “D” and all other months are numbers.

The two numbers printed after the month identifier are the exact day of the month on which the shellac was mixed. In our example that day would be 20. This can of shellac was manufactured on the 20th of July, 2010.

With this information at hand, there is no reason to purchase shellac that is past or very close to the date of expiration put forth by the company. This also gives you the assurance that the shellac you buy is good to go. Below is another can lid for you to work out.

Build Something Great!
Glen

5 Comments

Filed under Finish Techniques, Shop Tips

5 responses to “Decode Your Shellac

  1. a49model

    This will be stored in the back of my head. Thanks

  2. Glen,

    Thanks for getting the information from Zinsser and sharing it. I personally think the company’s move from a date stamp to a code was boneheaded at best.

    As to reducing shellac’s sheen, have you ever tried the Shellac Flat flatting agent? I tried it recently and had good results.

    Chris

  3. Mitch Wilson

    I finally succumbed to all of your cajoling and bought a can of Zinsser’s this past week. I was a little put out with the use of the code and so am quite pleased to have your timely post. My can is just under a year old, so not so bad. Does the shellac work well over an oil/varnish blend, rather just boiled linseed oil? I don’t mind popping the figure a bit more on some projects, say on a woodworker’s cabinet with some inlay and curly maple veneer.

  4. Charles Wilson

    Thanks for spreading the word. Now I know when to replace my Zinnser Shellac and don’t have to test it before each application.

  5. A good one for your Q&A section!

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