I hace some old jars of clear dope, and am not sure which are butyrate and which nitrate. Is ther some simole way to tell?   

Jim, I love ya, but I really would love it if the question I actually ask is answered. The jar of suspected Nitrate is all I have, and is what I want to use, so throwing it out is not ideal.

I have heard, that if you put the wrong thinner with one or the other dopes, the result curdles up. It would seem that someone can provide me with the combination to test the various bottles of dope.

BTW that flying wing you sold me flies great!

Jim, I love ya, but I really would love it if the question I actually ask is answered. The jar of suspected Nitrate is all I have, and is what I want to use, so throwing it out is not ideal.

I have heard, that if you put the wrong thinner with one or the other dopes, the result curdles up. It would seem that someone can provide me with the combination to test the various bottles of dope.

BTW that flying wing you sold me flies great!

Larry,

Nitrate thinner will NOT work in butyrate dope - at all!  Butyrate thinner works just fine in nitrate dope, so well, in fact, that there is no need to have any nitrate thinner on hand at all.  I can tell by smelling the dope if it is nitrate or butyrate; bring it to Warren's on Thursday evening and we'll check it out.

Why do you want to use nitrate dope at all???  Let me know how much you need (within reason) & I'll give you some butyrate dope.

Thanks Bill, that is just the information I needed.  Do I recall right that general purpose lacquer thinner is effectively Nitrate thinner and will react with Butyrate?

The reason I want to use Nitrate is that it can be used in place of Balsarite for adhering Coverlight covering.  Apparently, Butyrate doesn't have the heat activated adhesive quality that Nitrate does.  I have plenty of Balsarite, but I find that it turns dark brown after long exposure to the sun! Yukky!!! I had to repaint my Diesel powered Baby Clown because the entire wing outline had turned brown.

I do plan to get to Warren's this Thursday unless the weather is insanely hot.

Hi Larry,

Sorry to be so late but I haven't been online for a few days.  In Southern California at least, you can't get lacquer thinner that will work with dope anymore - thanks to our EPA.  I had never heard about using nitrate dope for adhering covering nor that nitrate has "heat activated adhesive qualities".  I have just never tried that since I don't use nitrate at all...just butyrate dope from the bare balsa through the final coats on the silkspan. 

Bill-
Do you add any additional plasticizer to Randolph A-1690 non tautening butyrate dope for model work??
Don

Hi Don,

I do add additional plasticizer (Dave Brown's Flex-All) using the amount recommended on the bottle.  I use the A-1690 clear from the bare balsa up through the covering with silkspan.  Over the open bays I use the tautening type butyrate (Randolph 9701) on the open bays only, brushing on three thinned coats to tauten the covering in the open bays.  I then spray on three or four coats of A-1690 with no added plasticizer, then some A-1690 with zinc stearate filler and still no additional plasticizer, sprayed on the entire airplane to be sanded and re-applied as necessary.  I then spray on a coat of Randolph Y-6100 with plasticizer added and add plasticizer to all subsequent coats of color and the final clear.

Adding plasticizer to the clear with the zinc stearate inhibits the sanding of the filler coats.  I also try not to spray much material into the wing root/stabilizer root fillet areas from the bare wood out to the final clear to avoid having the dope pull away from the fillets.  I use leather for the fillets and the dope adheres extremely well to the leather, but I still am careful.

Bill, I have heard that a drop or two of castor oil can be used as a substitue for plasticizer. True or Urban Myth?

Bill, since we are all asking questions here, what is the Y-6100 of which you speak. I tried to look it up on the Randolph site but could not find it. Thank you.

Hi Jim,

Sorry, I meant to show what the Y-6100 is...it is Randolph's Polar Gray.

Bill, I have heard that a drop or two of castor oil can be used as a substitue for plasticizer. True or Urban Myth?

I have heard that myth (fact?) too but have never tried it even with the full-scale airplanes since other specifically designated plasticizers are available and they don't cost much.  I'd be reluctant to risk a lot of labor & material experimenting with castor since the cost/benefit ratio doesn't justify it for me.

Bill

Thanks Bill, and thanks for the other info as well. I always read your comments and I always learn something new.

I have used castor oil as a plasticizer...in Nitrate clear, I'm pretty sure. It seemed to work, but it should also reduce the adhesive qualities of the dope. I would absolutely NOT use it on a stunter. Lifting fillets would probably be even more of a problem than usual.  Steve

Adding too much of almost anything we add to dope will reduce adhesion, both for base coat adhesion and inter-coat adhesion.  Too much plasticizer will definitely cause an adhesion problem as will adding too much silver paste to the clear (if you are using silver as the blocking coat.)  I know that most of the guys who use the silver dope blocking coats will just buy silver dope, but for use on full-scale airplanes I generally mix my own silver using aluminum paste and clear butyrate.  The ratio of aluminum paste to unthinned clear is not more than 4 ounces of paste to one gallon of unthinned non-tautening butyrate clear.  Probably more info than anyone needed or wanted but hey, at least you got your money's worth.