Hi Steve.
If it helps, I've only ever used rosin mixed with Stockholm Tar.
Dave
Hi Dave,
where do you get rosin and Stockholm Tar these days?
At the moment I am experimenting, by adding very small quantities of 30 grade motor oil, to a brew I have, of 50/50 Gugolz, #55/#64. Doing incremental tests, by adding a teaspoon plus, to the approximate 1Kg of G, then letting cool, and doing the small coin edge test, to get the right hardness/softness, for my current 5-7deg working area.
The motor oil suggestion, came from a well known mirror maker from the US. My aim to arrive at a mix, equivalent to G#40.
Hi Steve.
I have had a stock of rosin for some time so I don't know where to get it now but the Stockholm tar can be bought from most vet supply stores or saddlery/equestrian supplies. I use 7 parts rosin to 1 part S/t for 20° temp. An extra teaspoon of tar will soften 1 ltr mix a reasonable amount.
I'm sure it would work with pitch.
You want to use Gum Turpentine for softening not turps !
When you say gum turpentine, do you mean, pure turpentine, or is this something different? If so where does one source it?
Have tried motor oil (not impressed). Seems not to mix, for when the mixture was cooled, the pitch was as hard as ever, the oil located itself around the edge of the heating pot (aluminium hot pot). Problem mineral/not mineral combination?
Stephen.
Last edited by sopticals; 05-07-2012 at 03:05 PM.
Reason: spelling
I'm guessing it is pure turps, made fron pine resin/gum.
Smells very strongly of pine, I love it.
I don't remember but I think I got mine from Bunnings, I remember it being about twice the price of the regular stuff.
When you say gum turpentine, do you mean, pure turpentine, or is this something different? If so where does one source it?
Have tried motor oil (not impressed). Seems not to mix, for when the mixture was cooled, the pitch was as hard as ever, the oil located itself around the edge of the heating pot (aluminium hot pot). Problem mineral/not mineral combination?
Stephen.
As far as I know, gums turps and pure turps are the same thing. Don't confuse this with mineral turps for cleaning paint brushes etc. You can get it at any decent hardware store and is used for mixing quality timber furniture finishes.
Last edited by skies2clear; 06-07-2012 at 12:21 PM.
Reason: added info
Hi Steve.
If it helps, I've only ever used rosin mixed with Stockholm Tar.
Dave
I used to use pure turps, (seemingly, same as "gum turpentine"), in the sixtys, with beeswax, to temper my rosin/resin. I remember the aroma of the lap, was "outa this world (nice)". Not impressed with the aroma of Gugolz, but thats progress I suppose. Any way have tossed up whether, I should use the "pure turpentine", or " Stockholm Tar", to soften the Gugolz. The toss went the way of the S.Tar, for two reasons. Firstly, I know that the p.turps, is very "volatile",in which case the lap would not retain its new "softness level" for very long. Secondly, I would have to do a return journey, of at least 100km to aquire a supply. Fortunately, the local vet, just down the road, (less than 10minutes drive), had the s.tar on the shelf, so the deal was done. I assume the tar being less volatile will mean greater "softness" longivity, for the new lap. Looking forward to getting lap, and mirror reunited in the 5-8deg work enviroment.
I see still no mirror making subject has become a sticky yet.
Cheers
Yes, I've asked mike for a mirror making thread section. He offered to make this thread a sticky a while back. Perhaps a if a few more people raise it then it will happen
I'm guessing it is pure turps, made fron pine resin/gum.
Smells very strongly of pine, I love it.
I don't remember but I think I got mine from Bunnings, I remember it being about twice the price of the regular stuff.
Yes I meant 'turps' to mean `mineral turps'. You should be able top get Gum Turpentine from and hardware store.
Yes, I've asked mike for a mirror making thread section. He offered to make this thread a sticky a while back. Perhaps a if a few more people raise it then it will happen
Unless we read the thread, we don't know (and no we don't read every thread ). A pm to one of us Mods would of sufficed.
Hi Steve.
I have had a stock of rosin for some time so I don't know where to get it now but the Stockholm tar can be bought from most vet supply stores or saddlery/equestrian supplies. I use 7 parts rosin to 1 part S/t for 20° temp. An extra teaspoon of tar will soften 1 ltr mix a reasonable amount.
I'm sure it would work with pitch.
Dave
Thanks Dave,
I think the S/T is going to "hit the spot". Yesterday, did a melt mix of 1kg of a 50/50 mixture of Gugolz #55/#64, and about 150ml of S/T. I let this mix cool to the ambient temperature, (7deg C), and tested, failed the fingernail/edge of small coin test, as I could easily depress the cooled pitch surface, in a couple of secs, with forefinger. OK, overdone the S/T. Added another KG of #55G, to the "mess", and had a second run, (NO MORE S/T). Upon cooling, the coin test gave a 1/4" indent at 10sec, (temperature at the time 4deg C). Poured two sub diameter laps, (12" and 7"), with this new mix, which I shall call #40G. Armed with these new laps should be able to now carry on "winter season figuring".
Just a note on testing pitch. I like to leave samples for a while-fast cooling them under water doesn't seem to give a reliable test for some reason, tends to read too soft.
Hi Steve.
Stockholm tar can be bought from most vet supply stores or saddlery/equestrian supplies. I use 7 parts rosin to 1 part S/t for 20° temp. An extra teaspoon of tar will soften 1 ltr mix a reasonable amount.
I'm sure it would work with pitch.
Dave
Hi All,(and special thanks to Dave Brock),
The stockholm tar tip has provided me with a real breakthrough in my being able to continuing figuring my 22" and 25" mirrors at my current 4-10deg C temps,(working outside in my back yard). Previously with #55 Gugolz I was unable to successfully make any headway with figuring, due to the pitch laps being too hard.
Now with the right mix of pitch/stockholm tar have produced three very complient sub-diameter laps,(7",12.25" and 14"). With the use of these, I have brought my second 22"er, to a point where star testing, using the Ronchi eyepiece (133lpi) is the next step. I found with these large very (very) thin mirrors, that astigmatism during figuring presents a real problem,(if stoke is not quite right, one can produce what appears to be major "stig" within 3-5minutes). The good news is that the defects polished in can be polished out, (though corrective therapy takes considerable longer).
During the final 1-2 hours of figuring, while I was working with the larger 14" lap to remove some residual stig, and improve overall smoothness to the figure, I was greatly aided by the climatic conditions, gently raining, (greatly helped to lubricate the action between mirror and lap-was just using the minimum amount of CeO), temperature at 8.5deg C. The result, a very smooth finish. As I mentioned in a previous post I estimate the pitch hardness as equivalent to about #40G.
Also making progress with the 25"er, again coming in and out of stig problems but overall I am making headway and expect this optic to be ready for star testing soon.
Just like to report that I have finished figuring, (first iteration),the 25" f4.72 by 3/4" thick float glass mirror, after 33hrs of fighting all the contortions that astigmatism could throw at me.
The present spell of cool (7-8deg C) damp weather, has given me the ideal conditions to successfully use my #40G pitch laps, to gently move the mirrors figure in the right direction.(Neither of the 22"ers presented such a challenge, though "stig" did present in both but not so aggressively).
When using the 85lpi Ronchi test I found the 25"er very sensitive to the position of edge supports while on the testing rig, (if not exactly +-45deg from mirror bottom then the mirror would show physical warp as astigmatism). The further the edge supports from the ideal, the worse the stig appeared to be, but when placement of supports was correct, stig disappeared. Neither 22" was as sensitive to edge support placement.
Testing is done at night with temps around 5deg C so as to approximate those temps which one would experience, when mirror would be working when night viewing in my part of the world, Autumn/Winter/Spring seasons particularly.(Dosent get really dark here in Summer anyway). Now just waiting for the weather to clear so star testing can be undertaken.
Hi all,
here is a picture of a couple of laps I made using Ardit instead of using plaster. Ardit is a floor leveling concrete compound used before tiling of floors. I used it when I ran out of plaster one time and found it to be really strong and good to use. It sets quickly and just before it dries you can shape it with a rasp to get a good shape. A few coats of paint on the back and rim of underside and then add pitch. I used the larger one with hard pitch to polish my mirror and it turned out spherical right to the edge. The smaller one was used for figuring using soft pitch.
, came from a well known mirror maker from the US. My aim to arrive at a mix, equivalent to G#40.
Gum Turpentine.
do you mean, pure turpentine, or is this something different? If so where does one source it?
). A pm to one of us Mods would of sufficed. 
the fingernail/edge of small coin test, as I could easily depress the cooled pitch surface, in a couple of secs, with forefinger. OK, overdone the S/T. Added another KG of #55G, to the "mess", and had a second run, (NO MORE S/T). Upon cooling, the coin test gave a 1/4" indent at 10sec,
),
that astigmatism could throw at me.
astigmatism). The further the edge supports from the ideal, the worse the stig appeared to be, but when placement of supports was
testing can be undertaken.
