I occassionally solder wire connections on old cars but have no technical knowledge on the actual soldering process. Over the years I have read articles or "instructions" that sometimes state to use only rosin core solder and not acid core solder. Could someone explain in laymen's terms what is the "rosin" and the "acid" in some wire solder and generally why one would use one type over another? Thanks...Michael

Micheal, 'I can't give a technical answer but I have 30 years experience building electronic kits(Heathkits, now out of businessbut a great Co. in Benton Harbour Mich with terrific designs, wonderfullTech help)& they make it clear in their manuals to use & ONLY USE rosin core solder. My guess is that acid core is either destructive of the electronic process or dangerous. Its just a guess & expect that either John Regan or Ron Patterson will soon give the technical reasons. By the way I have several Heathkits still functioning three decades later including a Westminister chime clock with 3 inch digits & a desk top alarm clock using Beckman Planer gas tubes. You could go to Walmart & buy a digital alarm clock for under $15.00 thus the death knoll for the Heath Co.
Edward R. Levy

Rosin core solder is typically used in electrical work.The rosin flux will not cause future destruction to the soldered joints in copper wire.Acid flux solder is used on soldering jobs like a gas tank leak or some non electrical mechanical devise.The acid flux is very deep etching for a strong joint.Anytime you solder with acid flux,the job should be neutralized with water and baking soda.This will prevent the acid from constanly attacking the work.
A few tablespoons of Arm n Hammer baking soda in some water will make a good solution.

I agree with Darren. I am an antique radio collector and repairman, so take it from a good electonics background - never ever use acid core on anything electrical. Rosin core is acceptable, and remember, use a good quality gun, good clean tip and make all solder joints shiney. Dull joints are poor, the solder was not hot enough or the material being soldered was not clean. (rosin is a flux, not a cleaner) For electrical work, I always reccomend rosin core small diameter solder from radio shack. Acid core is just what it is named, Acid, and it it a great cleaner to prepare a surface, but unless nuetralized it continues to degrade a surface, and nuetralizing in electronic work is also not a great idea, so dont put yourself in that position to start with.

Rosin core really is to make a electrical connection,doesnt have much strength like acid core.
When I was growing up I wanted to buy some Heath Kit equipment like the weather station and such.But by the time I got old enough to work and earn a wage and buy the kit,they were out of bussiness. I have some old equipment from Bell and Howell that a teacher built takeing a course.A oscope,and a digital bench meter with the nixitubes.I like the stuff.GOOD quality.

Acid core solder in wiring ceeps on corroding the wire back into the covering. Fine rosin core works great. Even on a radiator they will claen the area to be soldered, tin it and then use a non acid core solder then clean off the acidic tinning solution and it keeps from turning green. be sure to heat your wire joint first and then apply the solder so as not to have a cold solder joint that can cause problems. If you are in an area where you want to keep the heat from the solder gun from heating up the wire to some other unit , either clamp a set of needle nose vice grips to it or use a needle nose pliers with a rubber band around the handles to hold them shut.

Just one thing to add, for what it's worth. Years ago I worked part-time in a musical instrument repair shop, where solder joints on brass instruments have to be very clean and tight. They used their own formula for flux which I found very effective. It is a mixture of glycerine and muriatic acid (50/50 as I remember) applied with a squeeze bottle that has a small tip like an eye dropper or a cattle syringe. The glycerine keeps the acid from running all over the place, and muriatic acid is a very effective cleaner of brass. As with any acid flux, protect your eyes.