Lead in Paint and Gasoline.

Why did they used to add lead to paint and gasoline? They took it out, to clean up the environment, or something like that. But why did they add to both these things to begin with? And really, I guess I’m asking, why don’t they need to now?


IIRC they added it to gas for to get it to burn more evenly. My extremely WAG is that they added it to paint to get it to spread more evenly or provide better coverage.
ETA, looks like I was wrong on both, but I got the answers before the edit window closed.
Lead in Gas
Lead in Paint

Lead (II) carbonate is a white pigment and lead chromate is a yellow pigment, so they were used in paints. Tetraethyl lead was used in gasoline to increase its octane rating. It still is used in airplane gasoline and racing gasoline.

Lead in gasoline prevents fuel from detonating as it is being compressed (as opposed to being cleanly ignited by the spark plug). Detonation is bad for engines. Running leaded gas allows cars to operate at higher compression ratios without detonating, for better performance and higher efficiency.

I don’t know the exact story behind the phase-out of leaded gasoline, but my understanding is that most passenger automobile engines don’t run at the high compressions that require leaded gasoline. I seem to recall that the introduction of leaded gasoline for passenger cars was more driven by marketing than anything else.

NASCAR used leaded fuel up until a year or two ago.

Aviation gasoline is still leaded, and contains a hell of a lot more lead than auto gas used to. This is a matter of major controversy today, as the EPA and other groups are trying to get lead removed from avgas, but there is no proven alternative for high-performance piston aircraft engines (yet).

Lead in paint was used because it was a cheap way of making paints that looked good. When lead was removed from paint, paints got either more expensive, or crappier-looking (depending on which route the manufacturer chose).

Lead pigments have been used for centuries because of the hugh-quality paints they create. Tetraethyl Lead is one of the most effective anti-knock compounds. It has been replaced by other anti-knock chemicals and better engine design.

So, while exterior house paint might have lasted you 15-20 years 30 years ago, now it doesn’t.

Tetraethyl lead retards detonation raising the effective octane rating of gasoline. It was cheaper than raising the actual octane content, and also allowed octane ratings greater than 100 (which would indicate 100% octane) for high compression racing and aircraft engines. It also reduced exhaust valve recession issues in engines prone to that.

Removing lead from gasoline required that the actual octane content be raised, or that the octane rating be increased with ethanol or MTBE, both of which are more expensive and less effective than TEL was, and also do nothing to reduce exhaust valve recession.

Better metalurgy cured the exhaust valve issue, and electronic ignition, fuel injection, and sophisticated computer monitoring and control have significantly reduced the octane requirements in modern engines. Computer modeling of cooling systems has reduced hot spots that used to cause detonation, and flow modeling also provides swirling induction that is less prone to detonation. Today you have box stock running compression ratios of 11:1, possibly higher. That would have been a “racing mill” in the 1950-60s when vanilla cars had 6-7:1 CR, and performance cars might push 9:1, and only hot rodders were going beyond 10:1.

Beyond the pollution issues, and incompatibility with catalytic converters, high lead levels would often cause combustion chamber deposits that could lead to the very detonation the lead was there to prevent.

Lead made for cheap paint pigments, especially white which most light colors have a lot of even if they don’t look even a little whitish. Titanium dioxide is the most common replacement, and it is a lot more expensive.

Leaded gas wasn’t phased out because of it’s environmental or health effects per se. Leaded gas will foul a catalytic converter in short order, and so when the clean air regulations instituted in the mid-70’s virtually required them, leaded gas ceased to be usable on new cars. There are other chemicals that now serve the same anti-knock purpose, but they either have their own environmental issues or have performance drawbacks.

Another side-effect of leaded gas was that it prevented wear on the contact surfaces between the valves and the cylinder heads. So some leaded-gas era cars would experience very bad valve wear when forced to use unleaded unless retrofitted with hardened valve seats or if lead-substitutes are added. To be perfectly honest, though, I’ve owned plenty of pre-converter cars and never used anything than unleaded in them and never had a problem-- I guess it could be that they were all retrofitted before I started accumulating them in the 90’s, but I dunno. Among some of the old timers I’ve talked to, it seems like the unleaded gas was often more a scapegoat for the already-frequent valve issues experienced by older cars.