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How to melt rosin?


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#1 4strings

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Posted 23 October 2005 - 01:14 PM

Some time ago (maybe years) there was some discussion about melting rosin and re-forming it. I have dropped at least two almost-new cakes of Tartini, *in their cases,* and had them shatter. I don't think those hard cases are such a good thing. I want to try to put each back together again, and put them on cloth or chamois holders, which I think will be safer for them. I'm planning to use a toaster oven and small metal measuring cup. What temperature should I use, and how long does it take? Is it necessary to stir at all? Does it sound like a reasonable procedure to line the measuring cup with foil, melt the rosin, stick the cloth on as it starts to re-harden, and peel off the foil? Will the rosin leak through any holes in the foil and make it impossible to get it out of the measuring cup?

In short, what pitfalls do I face?

Joan

#2 Danielle

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Posted 23 October 2005 - 04:13 PM

I don't know about Tartini in particular, but doesn't some heated rosin fumes tend to be toxic in some way?

#3 Oded Kishony

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Posted 23 October 2005 - 07:02 PM

google search for colophony (rosin)

Rosin is a brittle and friable resin, with a faint piny odor; the melting-point varies with different specimens, some being semi-fluid at the temperature of boiling water, while others melt at 100° to 120° C. It is very flammable, burning with a smoky flame, so care should be taken when melting it.

see the rest of the article here:

http://en.wikipedia.org/wiki/Colophony

At www.google.com

put the rosin in the toaster oven (in a metal or ceramic container - not plastic :-)
raise the temperature slowl, when you see it start to melt hold the temperature until it's all melted.

ecco la
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#4 DutchViolins

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Posted 24 October 2005 - 01:55 PM

There is a description for the procedure to remelt rosin in the booklet "A Luthier's Scrap Book" by H.S. Wake (page 18). Shortly it is said that:

the rosin is broken into small pieces and a metal container. No danger of fire when a electrical heater is used. As soon as the rosin starts to melt continue with adding new pieces under continuous stirring. Stir gently untill all rosin is molten for good mixing all the different brands. Wake is pouring this out in a previous prepared and pre-heated cardboard container (dimensions: 2 X 1 1/4 X 5/8 ") holding the metal container with pliers. The box(es) should not be touched or disturbed for at least half an hour after having poured out the rosin. Rough sides can be smoothed and polished by passing over a clear flame.

For full text consult H.S. Wake's article.
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#5 Andrew Victor

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Posted 25 October 2005 - 10:53 AM

I once melted a broken cake of Tartini Green cello rosin and must have done it too hot, because it never worked properly thereafter.

I have been successful shaping aluminum foil to the desired cake shape, inserting all the broken rosin and heating it in a toaster oven at the lowest temperatuire that will melt it - less than 200°F.

As soon as the top is smooth I turn off the heat and let the caked cool in the oven. This has worked a number of times and better than any other method I have tried in years past.

Andy

#6 4strings

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Posted 26 October 2005 - 10:14 AM

OK, thanks everybody! For some reason I haven't been able to get Maestronet to load for a couple of days, but I'm going to give this a try today. Will report back--

Joan

#7 pandora

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Posted 26 October 2005 - 06:02 PM

I like using a cast iron fry pan on top of the stove - that way, I figure, if it bursts into flame I can slap the lid on and/or carry it outside instead of having to deal with a burning toaster oven. The bottom of a spice jar makes a dandy base for a mold of tin foil, and yes you can pick the sides off afterward. High priced rosins probably do take on different qualities if remelted, but with the cheap ones who worries? The temperature is important - ask any candy maker, the only difference between soft caramel and hard toffee is the temp you let the sugar syrup reach. Does anyone know if a slow vs a fast cool-down is preferred? It makes a difference with bonbons, so I'll bet it matters for rosin too.

#8 4strings

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Posted 26 October 2005 - 07:49 PM

OK, I went with the toaster oven, because I think I can control temperature better, and because the heat is general and not applied only to the bottom of the rosin. I started with foil in two pieces lining a votive candle holder, one for the bottom and one for the sides. Oven set at 200-210 (toaster oven accuracy not guaranteed), which is in the neighborhood of 100C, which the encyclopedia article said was rosin's melting point. The rosin took maybe 30 min to melt; I put in a little at a time, not knowing whether I might get a lot of air holes if I tried to do it all at once. The rosin got into the narrow crack between the two pieces of foil, which made it hard to peel the foil without losing some rosin. Also, I couldn't readily get the chamois down onto the melted product. I got it close, turned the foil-wrapped cake out of the candle holder, peeled the excess foil off, and pressed the chamois to the soft rosin before it got too cold. Not bad. Not great, but not bad. The top had a big dip in it, however, and everything looked -- well, sort of sloppy/saggy.

Next attempt, on another cake: Made a foil collar and laid it directly on the chamois, with a couple small chunks of rosin in it. Same temp. Rosin leaked out under the foil, a little. Meanwhile, worked with first cake, putting another foil collar tightly around the cake, then folding the chamois up a little and stuffing the whole thing firmly into the votive candle holder. Re-melted this: surface entirely smooth, rosin well adhered to chamois, figure it's good enough.

I had pulled the second cake out and let it cool a little while cake #1 was melting again. Chipped off the little leaks, placed rosin cake assembly, including foil, chamois and all, into votive candle holder, added the rest of the rosin chips, and slowly melted it again. Right now it's all cooling slowly in the turned-off toaster oven, as Andy suggested. As far as shape and usability goes, it should be fine. The chamois never seemed tempted to burn; I kept it away from the heating elements, and it feels just as soft and pliable as ever. I wonder about the properties of the rosin -- whether it will still work like Tartini. But if it doesn't, well, I never would have got any more use out of these cakes anyway, if I hadn't tried this.

For the record, I noticed hardly any fumes whatsoever. Maybe because I used such a low temperature.

I think in future I will only buy the mini cakes. They come with cloth holders, which gives them some shock absorption, and it takes ages to get through a cake of rosin anyway. And if rosin really does have a distinct shelf life, I can't imagine anybody getting through a full-sized cake in a year or so unless they're sharing with half the violin section.

Thanks again, everyone!

Joan

#9 Michael Darnton

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Posted 26 October 2005 - 07:57 PM

You have to look on rosin as a challenge. I've seen more than a few professional players who work to keep the top of their rosin level and un-chipped by working around evenly rather than making a trench, and not letting the frog ferrule touch the cake. The best I ever saw was a wafer about 3mm thick, still in its cloth, level, with no chips around the edge. Me, I'm more likely to drop it in the first week, and use little pieces from there on.
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#10 4strings

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Posted 26 October 2005 - 10:47 PM

That's me, all over. I had one cake of rosin for something like ten years, being out of the loop as far as rosin fashions go. Rosin was rosin. It was Hill dark, in cloth. I've never broken any rosin before this Tartini. Maybe I'm getting old and careless...




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