20mm (.7 inches roughly) glass signal mirror the size of a 20mm button compass

Would a signal mirror this small be effective at signaling up to 5-10 miles? I read on this site somewhere that size plays a role in distance, is there a rule of thumb on size for distance?

If I cut down a piece of old mirror and polished up the edges, coated the back in rubber and packed it along would it be almost as effective as my traditional signaling mirror, minus the aiming hole of course?

The reason I ask is the Rat Cutlery fire steel has a small capsule built into the handle that would fit something like this, I think it would be very handy to be able to fit compass, mirror and whistle in this little compartment. I could probably stuff the remaning space with a vacuum sealed cuben fiber tarp to take the place of an AMK heatsheet for wind and rain protection.

What do you guys think, ludicrous?

Also, have you ever seen anything manufactured this small?

OK, this one made me smile.

(How about stuffing the handle of that fire stick full of dry tinder so it works as an emergency fire starter?)

A mirrorlike that would be similar in size to the inside top of the so-called "5 in 1 Survival Whistle." See: http://beprepared.com/product.asp_Q_pn_E_CM%20W400_A_name_E_[[ProductNameURL]]

I've got a couple, which I have in kits, mostly because I like the whistle with the hollow inside for inserting some makings for fire. The part of this whistle I like least is the so-called signalling mirror. It's not a mirror, but seems to be a piece of shiny silver cardboard like one might find in a frozen food package.

A real mirror as you propose is likely to be a lot more effective should the need to signal arise. A larger mirror is probably going to be more visible, it's going to reflet more light. But the smaller one should be better than nothing.

You could use the 19mm 4-6 wave optical flat mirror available here;

http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productID=2077

although aiming the mirror would probably be very tricky although not impossible. Higher precision mirrors are available for bouncing laser light around without the beam diverging but they are considerably more expensive.

It would be an interesting experiment if you could compare its performance against a commercial polycarbonate aiming mirror you can pick up for around the same cost.

19mm circular flat mirror = 283mm squared
Typical Adventure Medical Kit Rescue mirror = 3500 mm squared

So the 19mm will reflect less than 12.5 times less light or probably around 10 times (assuming the 19mm mirror is more efficient). The 19mm beam will probably be less divergent than the commercial polycarbonate mirror because it will have a flatter surface.

I would have to say the 19mm mirror wouldn't be as effective mainly due to the aiming problem and the reduced size of the mirror.

Well, folks have been rescued using the hologram on a credit card as an improvised signal mirror. That's pretty darn small. Far from the best, but better than nothing.

True, if you are looking for something to fabricate a signaling device in the field. For planning a 20mm glass mirror would be better than many other options and would carry easily, but it should be considered a back-up. You might want to get outside and do some empirical testing to see for yourself.

Actually it wasn't the mirror that made me smile.
Cuben fiber is the cloth used for the spinnaker sails of modern racing yachts. It is very strong, light and all that, very techie stuff. It is a carbon and polyester fiber laminated fabric. Carbon for strength, polyester for flex.
Yes, very strong and light, also quite pricey.

And yes it is true the ultralight backpackers are trying it out for tents, tarps and hammocks. (Even though there are still some slight problems with the carbon fibers fatiguing when sharply folded.)

However, I think he would have a problem stuffing it into that small of a capsule, especially when he is talking about using it to fill waste space.

(If he succeeds I want to see pictures, and then I might invest in the idea.)

I'm going to cut some mirror up\order it and test it with a partner using 2way radios. Ill let eveyone know how it turns out.

In regards to the cuben, it is pricey. Its about $19 a square meter direct from cubic tech with a minimum order of 9 meters or about $26 per square yard from a fabric supply. I made a rain shell out of the .33 oz stuff using a tape adhesive from 3m and it is very light. Total weight is a little over 1oz and very warm. %100 waterproof and windproof but not breathable, think sauna without incoporating pit zips.

This fabric gets people laughing, my family thinks its funny im making bacpacking gear out of "cuban garbage bags" but it really is great stuff.

This is one reason I think 'little'of knives with hollow handles or tang compartments to carry kit.
People start tailoring the gear to the premise of fitting, not working. This was a fad on survival sites some years back. I think the guy who announced a spent .22LR shell was his signal whistle epitomy of this trend. I never received a reply to my question 'do you use the shell AFTER you kill a charging grizzley bear with your M6 with the fancy paracord forearm or just use one for making a fire?
People are buying $350, 2 lb, 1/4' thick knives and stuffing them with crackerjack prize kit.

No offense but the mirror would be used to blind the bear, not shoot it. The spent .22Lr is for whistling dixie afterwards.