I have a question for those of you who are experienced using dry ice for fog/smoke effects:

How long will a chunk of dry ice remain viable for making fog/smoke?

For instance: if I wanted to make a cup produce smoke could I put a piece of dry ice in the bottom of the cup, then cover the cup with a handkerchief which has a concealed ear syringe full of warm water hanging on a loop of thread, give the ear syringe a slight squeeze so that the warm water would contact the piece of dry ice, then uncover the cup (pulling away the ear syringe on the loop of thread under the cloth) and have "smoke" coming out of the cup.

If I loaded the piece of dry ice into the cup half-an-hour before performance would it still produce fog/smoke or do I need to use it sooner than that?

How long is a piece of string?*

How big is your "chunk" of dry ice?

Aside from size (which, in this case, matters), the other major determining factor is ambient temperature. Dry ice will last longer in a cold storage locker than it will in a sauna.

Tnen there is the matter of insulation. Dry ice will last longer in a heavy styrofoam cup than it will in a metal container.

Conclusion ... your question is impossible to answer theoretically and easy to answer via simple experimentation. Shut up and try it.

Good thing I'm feeling patient today.

Sid

*The usual answer to this one is twice half its length which is a non-answer to a non-question.

Thanks, Sid.

I am properly chastised for my very vague question .

The "chunk" of dry ice is the size of a "chunk" which will fit in the bottom of a cup , of course.

Thank you for your patience , oh wise one .

To answer from a lab point of view. It is dependent on the quality of dry ice, some is better than others. I can store dry ice from some companies over the weekend in a polystyrene box no hassle, others barely last the night.

Good dry ice should be alright for half an hour in a cup, I would suggest getting a circle of polystyrene and sticking that onto the base of the silk, as this will help by acting as a lid. The best thing to do is experiment. Maybe try a number of small chunks (greater surface area when the water hits is) as far a temperature goes, after half an hour the water won't be warm!

PS my piece of string is 9102mm today under constant strain and measured at 25C

The best thing would be to test it out and see if it works. If it doesn't then you know you have to do something else to keep it cold. mgical has some good points and ideas to try if it doesn't work.

David,

Dry Ice usually is sold in two ways (at least in my area) as chips, or a block.
I forget the size/weight of the bag of chips I got, it was almost 2 years ago, but it was fairly large, 20lbs I think. $40. It lasted 3 days outside in a coleman cooler over Halloween. I used most of it for my fog chiller, but usually I just use regular ice because it's easier to get and cheaper.

The thing about dry ice is that it's frozen carbon dioxide, not water, and it doesn't melt, it sublimates , or goes directly from solid to gas form.
Be careful not to touch it, ever - you will "burn" your fingers. It is extremely cold: typically -109 degrees farenheit. Use tongs and gloves. If you put it in a cup you drink from (probably not a good idea) , make VERY sure you don't get that "ice cube" in your mouth or worse, swallow it.

Sid, you made good points but that was uncalled for. He specified a cup, so how much variation is there going to be ? He might get 15 minutes from it, or 45. It's not like it's a difference of hours.

The only point that I was interested in making was also made by james_magic. Instead of asking, a bit of experimenting would be more useful and might also serve to eliminate clutter.

Sid

I have a similar problem that I've been working on for years. I have a cauldron that I would like a fog or mist to roll out over the rim, although I'm looking for this to happen over an extended period of time, say half an hour or so. I need it very portable, so a standard fog machine doesn't work.
In my experiments with dry ice, there are two main problems.
1) If you put dry ice into a limited amount of water, such as a cup (or a cauldron), the amount of fog diminishes very quickly. The dry ice quickly drops the temperature of the water, and as the water temperature drops the amount of fog produced drops. If you can keep the water at a relatively constant temperature the amount of fog will drop as the chunk of dry ice diminishes.
2) The fog is heavy, so if you have it in a cup the fog it wants to sit in the cup rather than roll over the top.

With the cauldren I used to use (big antique washpot), I solved the water temp problem with a few electric water heaters (you know, the ones you stick in a cup of coffee - but bigger). Kept it going until the Ice ran out.

Azrael

I would recommend having a dehumidifier if you want to keep dry ice for long periods of time, because the drier it is, the longer it takes to sublime(sublimate).

Alchemist, have you tried the small electronic fountain foggers?