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Comment by gniv | Hacker News Reader

I never thought about the weight of the paint. I asked LLMs how much a coat of paint of 120 microns would weigh. Between 5 and 8 pounds apparently.

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Weight of paint depends a lot on the pigment. Some pigments are pretty dense a lot pigments are various types earth or metal oxides. Think like iron oxide (a dark red or brownish yellow) there are even heavier pigments. Organic pigments tend be lighter. Titanium dioxide is a very common pigment though since it is the main white pigment used for paint these days. If you have felt weight of titanium white vs lead white (only pretty much used for art these days) for instance you can tell the difference.

Then you have some things that are not a pigment per se but are there to help with flow and other things but are not light either like kaolin clay. Also they can be used as filler to make the paint cheaper if used in excess.

At one point when airlines were concerned about rising fuel costs, several switched to a largely unpainted livery, with the polished aluminium otherwise being uncoated (or possibly with some protective clear coat), for weight savings, which were given as ~100 kilos / 200 lb if memory serves.

Those of us who remember leaded paints also recall how distinctly heavy cans of white paint, or any paint with significant amounts of white blended into it, were.

Would you believe a random Internet comment/site for that answer?

I wouldn't, so I also wouldn't believe an LLM trained on those questionable sources.

Haha absolutely first they censored unwanted content and now they feed the remains to the almighty.

Not to speak about the discredited personas on Wikipedia unable to change their decried vita entries..

I didn't expect anyone to politicize the weight of paint.

Both Gemini and ChatGPT gave quite detailed answers showing the input values, the intermediate calculations, the assumptions made. I chose to only give the final result here. But see another comment from me with details.

Have you ever picked up a can of paint?

Do you not allow the solvent to evaporate when you paint things? Must be a bit messy.

I’ve only used water based paints at home and thought most of the weight was water which evaporated on drying

Since folks are downvoting this comment, here's what Gemini told me, and which sounded reasonable to me. Let me know if something sounds wrong:

Paint thickness: 120 microns (0.00012 meters)

Typical car surface area: Assuming a medium-sized sedan, we can estimate this to be around 15 square meters (161.46 square feet).

Paint density: This varies based on the type of paint, but we'll use an average value of 1.2 g/cm³ (1200 kg/m³) as a starting point.

Volume = thickness * surface area = 0.00012 m * 15 m² = 0.0018 m³

Weight = density * volume = 1200 kg/m³ * 0.0018 m³ = 2.16 kg

ChatGPT was similar but chose 1.3 g/cm³ as the paint density.

Did you have it show its work?

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