xraymymind Posted September 20, 2019 Report Share Posted September 20, 2019 Hey all. this is a question to all of you out there who add Calcium Oxide, or Hydroxide to your varnishes on cooking. I am wondering what the actual reason for doing this is: what qualities does the Lime add to the varnish? i have made a great varnish cooking lime in with Greek pitch, but was never actually sure what benefits/drawbacks adding the Lime actually had. I have also heard of people cooking it in with their Linseed oil prior to amalgamating with the GP. Why add the lime to one and not the other, etc? Let the can of worms be opened! Quote Link to post Share on other sites
Johnmasters Posted September 21, 2019 Report Share Posted September 21, 2019 10 hours ago, xraymymind said: Hey all. this is a question to all of you out there who add Calcium Oxide, or Hydroxide to your varnishes on cooking. I am wondering what the actual reason for doing this is: what qualities does the Lime add to the varnish? i have made a great varnish cooking lime in with Greek pitch, but was never actually sure what benefits/drawbacks adding the Lime actually had. I have also heard of people cooking it in with their Linseed oil prior to amalgamating with the GP. Why add the lime to one and not the other, etc? Let the can of worms be opened! Both limed rosin and limed linseed oil are old and traditional (cheap) components of varnishes in the first half of the 20th century. The calcium rosinate is less acidic than plain rosin and is also tougher. Quote Link to post Share on other sites
David Burgess Posted September 21, 2019 Report Share Posted September 21, 2019 15 hours ago, xraymymind said: Hey all. this is a question to all of you out there who add Calcium Oxide, or Hydroxide to your varnishes on cooking. I am wondering what the actual reason for doing this is: what qualities does the Lime add to the varnish? i have made a great varnish cooking lime in with Greek pitch, but was never actually sure what benefits/drawbacks adding the Lime actually had. I have also heard of people cooking it in with their Linseed oil prior to amalgamating with the GP. Why add the lime to one and not the other, etc? From what I've observed, this is mostly done with rosin varnishes to reduce the high acidity of the rosin. In my own experiments, a rosin-linseed varnish seemed to degrade pretty quickly if high acidity remained. Quote Link to post Share on other sites
Emilg Posted September 21, 2019 Report Share Posted September 21, 2019 43 minutes ago, David Burgess said: From what I've observed, this is mostly done with rosin varnishes to reduce the high acidity of the rosin. In my own experiments, a rosin-linseed varnish seemed to degrade pretty quickly if high acidity remained. I have wondered how resins and oils can be acidic, as acidity is defined by H+ ions in aqueous solution. I suppose it's because wood, resins, oils and even air always contain a few % moisture to allow acidic behaviour. Quote Link to post Share on other sites
Felefar Posted September 21, 2019 Report Share Posted September 21, 2019 Oils and resins are really fatty acids, so adding lime leads to saponification. Saponified oils and resons have drastically different properties than the raw fatty acids, although not as much as simpler fats like e.g. palm oil (look at your soap, it will most likey contain sodium palmitate, which is the reaction product of lye and palm oil). Calcium soaps tend to be hard and practically insoluble, which is just what we need for varnish. Addendum: Aqueous solution is not needed to call an organic acid an acid, it is enough that the formula contains one or more COOH groups. Quote Link to post Share on other sites
JohnCockburn Posted September 21, 2019 Report Share Posted September 21, 2019 2 hours ago, Felefar said: . Calcium soaps tend to be hard and practically insoluble, which is just what we need for varnish. Boat varnish, maybe Quote Link to post Share on other sites
Michael_Molnar Posted September 21, 2019 Report Share Posted September 21, 2019 3 hours ago, JohnCockburn said: Boat varnish, maybe Is your violin varnish soft? Mine can be somewhat brittle. Quote Link to post Share on other sites
J.DiLisio Posted September 21, 2019 Report Share Posted September 21, 2019 In my experience liming makes a tough varnish that wears very little. Not ideal for antiquing. Quote Link to post Share on other sites
Michael_Molnar Posted September 22, 2019 Report Share Posted September 22, 2019 Calcium is an auxiliary drier that increases oxidation. Some varnish makers claim it gives a surface shine. And, yes, it reduces varnish acidity that can attack organic pigments. Quote Link to post Share on other sites
Michael Szyper Posted September 22, 2019 Report Share Posted September 22, 2019 21 hours ago, DoorMouse said: In my experience liming makes a tough varnish that wears very little. Not ideal for antiquing. My varnish is heavily limed and responds perfectly to alcohol. That is what I use for wear imitation. Quote Link to post Share on other sites
J.DiLisio Posted September 22, 2019 Report Share Posted September 22, 2019 1 minute ago, Michael Szyper said: My varnish is heavily limed and responds perfectly to alcohol. That is what I use for wear imitation. I meant to say that it doesn't have the fragility you can achieve with an unlimed varnish. It doesn't chip off easily with a fingernail. Quote Link to post Share on other sites
Michael_Molnar Posted September 23, 2019 Report Share Posted September 23, 2019 FWIW, @Roger Hargrave does not add lime. Quote Link to post Share on other sites
Jim Bress Posted September 23, 2019 Report Share Posted September 23, 2019 1 hour ago, Michael_Molnar said: FWIW, @Roger Hargrave does not add lime. Varnish discussion aside, I’ve read “Making a double bass” PDF from Roger’s site several times. It should be required reading. Thanks for linking the thread, which I only read as it was being written. I’m sure there are many other gold nuggets in buried in the 32 pages. Quote Link to post Share on other sites
joerobson Posted September 23, 2019 Report Share Posted September 23, 2019 Adding lime to colophony based varnishes cannot be considered as a factor on it's own. When (and if) to add lime...and how much...is also a function of the way the oil and resin were prepared and the end goal of the varnish maker. As with most of violin making it is both simple and complex. on we go, Joe Quote Link to post Share on other sites
uguntde Posted September 23, 2019 Report Share Posted September 23, 2019 The reaction of rosin and linseed oil is chemically a cross-esterification. Lineolic acid gets attached to abietic acid. In solution such reactions are base catalysed. I assume that something like this is happening in hot rosin, especially, as the lime is added in water. Lime light just catalyse the ester cleavage of the abietic acid. Industrially anothet catalyst is used which I need to look up. This is just an assumption, as I know little about such chemistries. Quote Link to post Share on other sites
Michael Szyper Posted September 23, 2019 Report Share Posted September 23, 2019 If you want to neutralize acidity without hardening the resin too much you could also use potassium or sodium hydroxide and/or potash. I like to add 1/3 of the acid number equivalent, otherwise things get too hygroscopic. (By liming the rosin you actually are making soaps). Quote Link to post Share on other sites
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