tenneyguy Posted June 18, 2021 Posted June 18, 2021 Is shellac, flaked or powdered, at all hygroscopic? Need it be stored in airtight jars? I bought some from a guy who shipped it in a plastic bag. It is one hard chunk in there, with a little powdering around the edges. Thank you for any help.
davidh Posted June 18, 2021 Posted June 18, 2021 (edited) Heat makes it sticky, and alcohol dissolves it. It is hard to powder. As far as I know it does nothing to, with, or for water. Edited June 18, 2021 by davidh 1
tenneyguy Posted June 18, 2021 Author Posted June 18, 2021 Heat makes it sticky, and alcohol dissolves it. It is hard to powder. As far as I know it does nothing to, with, or for water. Thank you! Thus shellac is not to be recommended as a binding material, though it is mentioned in some of the literature?
stix Posted June 18, 2021 Posted June 18, 2021 . . . Thus shellac is not to be recommended as a binding material, though it is mentioned in some of the literature?.Well, according to PyroData: https://pyrodata.com/chemicals/Shellac Description: Shellac has been in use as a binder and fuel for many centuries, but has been gradually replaced by Red gum. However, it is still sometimes claimed that shellac is a superior fuel for use in coloured compositions. It is a somewhat brittle but strong resin that dissolves in ethanol and acetone, albeit slowly..So, I guess it can still be used as a binder and fuel, but maybe there are much better choices available now. Dunno... I have some Shellac but have never used it. 1
Arthur Posted June 18, 2021 Posted June 18, 2021 Shellac is both a binder and a fuel. It is activated by organic solvents, not water. It's popular with chlorate comps and usually it seals comps that may be water sensitive. 2
davidh Posted June 18, 2021 Posted June 18, 2021 (edited) Shellac would be what I would call an "advanced" binder. Be prepared to have problems with it when you first start using it. You have to add just the right amount of alcohol to it and wait for it to soften or dissolve which makes it tricky to use. I use it in lance formulas that are not granulated with alcohol, so I don't use it as a binder. Edited June 18, 2021 by davidh 2
Mumbles Posted June 18, 2021 Posted June 18, 2021 I don't really like it much as a binder. It has a tendency to skin over and slow evaporation pretty easily. Once dry, the stars were fine though. I much prefer red gum or phenolic resin or something. For something like lances where the comp is dampened more than wet, it would probably be just fine though. 1
davidh Posted June 19, 2021 Posted June 19, 2021 (edited) I once made pillbox stars using a 90/10 barium chlorate shellac formula. I added the prescribed amount of alcohol to the mix. It was like slightly damp sand. It would not stick together no matter how hard I pinched it into the paper sleeves. So I added that much alcohol again, and again, it was like slightly damp sand. I added a third amount, and then it became like putty. I thought I had it and started making stars. When I went to make the fourth star, the mix had turned into a literal slurry. I could pour it. And it was pouring out of the three stars I had already made. It was quite the mess. So I let the comp dry out over night, and in the morning it was a solid sheet. I added the prescribed amount of alcohol again in hopes of getting back to the correct work-ability, but the comp remained hard. The amount of alcohol was not enough to dissolve the shellac, only make it sticky. So I added a bunch more alcohol and turned it back into a slurry. Then for the rest of the day I stirred it on the hour until it thickened to the point I could make stars with it. I made those pillbox stars, and that was the LAST TIME I used shellac as a binder. The end. Edited June 19, 2021 by davidh 1
Arthur Posted June 20, 2021 Posted June 20, 2021 Shellac was popular or even essential in the days of chlorate comps. It is fuel and or binder with no chlorate incompatibilities. I see less use of it in modern comps. it's soluble in costly organic solvents and only dissolves or dries very slowly so it's an added expense in materials and time BUT if you need it you really do need it.
justvisiting Posted June 20, 2021 Posted June 20, 2021 I had a very similar experience to Davidh when making Weingart's green box star formula, 9 parts barium chlorate to 1 part shellac. The same basic formula is also listed under 'Exhibition Pumped Stars' with 1/4 part dextrin additional. The green is the greenest I've seen. A box star is made differently than other star types. The dampened composition is pressed by finger pressure into a sleeve or 'pillbox' that has a piece of black match in it, which hangs out both ends. In this case, the alcohol dampening does not need to be so much as to make a firm star as would be necessary otherwise. In my edition, Weingart didn't specify the amount of alcohol to use. The star only needs to be 'just' consolidated enough that the comp doesn't fall out the ends (my words). The alcohol would easily wick away through the sleeve while the star slowly hardened. I attribute my failure to trying to use the formula incorrectly, expecting immediate evidence of binding. That's just a guess. Some stars using alcohol I have made were so crumbly I could barely form them, but they dried as hard as rocks. Those stars also had a chlorate oxidizer. I wonder if the soupiness comes from the water of crystallization in the barium chlorate, somehow working with the alcohol to make the mess? Another situation that can occur is that shellac powder stored for a very long time can polymerize and become insoluble in alcohol. I had this happen to me. I contacted the shellac company and their chemist told me this. I expect that the pumped star formula, dampened with water would work well even if the shellac had undergone polymerization, but I haven't tried it.
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