Re: Does color affect the rate that ice melts?

For ice to melt, it has to take in energy from the surroundings, in the form of heat. Now heat can be taken in from the surroundings in two ways. It can flow in directly by contact if the ice is touching something hot. Or it can flow in as heat radiation from a distant hot object. Sunshine is the most obvious and most important source of radiant heat, but nearby fires, or automobile engines, or even warm houses, might contribute a bit of radiant heat.

The colour of an object will not affect the contact flow of heat. But it can affect radiant heat quite a lot. White, or highly polished, or light coloured objects reflect most of the radiant heat, just as they reflect light. Only a little bit would be absorbed, so not much heat would be taken in to help with the melting. But dark coloured objects absorb most of the light or heat that falls on their surfaces, and black objects absorb nearly all of it.

So in most cases, dark coloured ice will melt more quickly than light coloured ice, if it is in the same situation. Especially when the sun is shining on it!

There are two extra points that need to be made.

Firstly, there is not an exact match between absorbing visible light and absorbing radiant heat. Radiant heat largely involves infrared light, and some substances which reflect visible light (light coloured) actually absorb infrared light. So you can not exactly tell by the colour, though it is usually a good indication.

The second point is that if you look closely, you will find that ice is always white (or transparent). With coloured ice, the material that is making it coloured is separate particles. As far as melting is concerned, that does not really matter: the separate particles within the ice are what warms up when they absorb light or radiant heat, and they melt the ice by contact from within.

Greetings from a 40 degree (i.e. 104 American degrees) summer day, where there is not much ice of any colour around.

John