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Topic: ...which type of mirror is best?
Message: Posted by: Huw Collingbourne (Jun 27, 2002 01:50PM)
As I've mentioned elsewhere I am starting (in a modest kitchen-table way) to experiment with mirror illusions.

I am told (by a non-magician physicist friend) that normal back-silvered glass mirrors are far from ideal since a) the depth of the glass may 'show through' in certain effects and b) the glass itself may cause visible degredation in image quality when multiple mirrors are used, each mirror reflecting into the next in series. He tells me that front-silvered mirrors - that is, mirrors made with a thin layer of silver over the *front* of the glass - is best and this is why these mirrors are used in sensitive optical devices such as some telescopes. There are two disadvantages though. First, while it is possible to make small front-silvered mirrors at home without too much expense it is probably impractical to make large mirrors in this way and it would be too expensive to buy them. Secondly, the silver can easily be damaged by scratching.

Is there an alternative? That is, a mirror with the desirable optical qualities of a front-silvered mirror but with the resilience of a conventional back-silvered one?

best wishes
Huw
Message: Posted by: RiffClown (Jun 27, 2002 02:30PM)
If you can find a sheet of mylar that is silvered, your only challenge is keeping it perfectly flat(taught). A single thickness may not be opaque enough but a double thickness usually works well. A single thickness works pretty good for candle under water effects etc.

Hope this helps.
Message: Posted by: Ray Haddad (Jun 27, 2002 03:02PM)
Huw,

For extremely fine optical purposes, he's correct. For our purposes, you'll never see the problem.

In magic, we most often use mirrors in a cruder fashion than telescope makers.

We use them quite openly such as when walking through mirrors or penetrating them with pencils, swords or silks. For these purposes, they can do a double refraction without any concern.

For hiding things, we almost always use a confusing pattern to reflect. This has the effect of drawing attention from the mirror and hiding its presence entirely in doing so. Used this way, the double refraction of less than 1/8 inch is impossible to detect.

Even solid colors will work. The only problem with solids is that the mirror edges are often detectable.

Front surface mirrors can be found in scrap photocopiers that have long focus imaging systems. The kind that enlarge or shrink a document use them to keep from having a ghost image of a document. I've seen them as large as 8 by 10 inches.

Laser security companies use them for sending a beam into a pattern for marking perimeters.

As an adjunct to this question, I would recommend that you not use glass mirrors at all since they can break even with the most careful shipment and handling when on the road. The are also quite heavy. Try locating Perspex(tm) or Plexiglass(tm) mirrors. The cost is nearly the same but they are virtually unbreakable in a magic environment.

Best,
Ray
Message: Posted by: MichaelSibbernsen (Jun 27, 2002 09:51PM)
Being an astronomer, I can tell you that front surface mirrors would definitely not be the best route. As you mentioned, they can scratch easily; that is an understatement. Just the act of wiping the dust off with a lens tissue can damage the mirror. In other words, much much too delicate for general use. You can of course have applied a silicon dioxide coating on the mirror, (like I have on my 16" Dobsonian Telescope), but why on earth go to that expense.

Ray is quite right, the "problems" of rear surface mirrors would rarely show a problem in magical effects. To counteract this so-called problem (which really does not exist) is to actually go the opposite direction. Use cheapo mirrors (like full length door mirrors) from Wal-Mart. Because the glass is thin, double reflection would be very small. You then reinforce the thin mirror by mounting on a piece of wood with a thin layer of adhesive like Liquid Nails. Not only does this make for a durable product, but also has the side benefit of giving you something to attach brackets, hinges, and straps to for construction.

I have not worked with Plexi Mirror so I really can not comment, but I have worked a *great deal* with regular plexiglass, lexan, etc. and can say that under even normal use it can scuff up easily and degrade its visual quality. Care needs to be taken with its use.

As for the mylar suggestion, keeping it flat is indeed absolutely key. In fact, best is to adhere (with Spray 90) the material to a square of sheet metal. This makes for a low cost, very durable, extremely thin product.
Message: Posted by: Magicduck (Jul 1, 2002 01:52PM)
I make a number of effects that use mirrors, in a way that hides a load. I agree that for a magician's purpose, one need not worry too much about "perfection" of the image. I do have a couple comments about what Ray and Micheal said.

1. As far as hiding edges, this can be tricky and is usually accomplished, if they are at top and bottom, with some type of bold line that appears to be an X in the unit. If the mirror edges are in the sides, that is easier to conceal in a a pattern or even in dark felt fabric. I make sure I sink the mirror into the walls, so the edges are concealed.

2. As far as mylar, I have used this for mirror glasses and small, easy to protect objects. My thought is it would be hard to use on a larger device that would conceal an animal.

3. I have, like Michael, always used glass stuck firmly to door skin or plywood. Only ever had one break...when it was dropped from 3'. I like the reflection better with glass, and the lighter refraction, than has been my experience with the plastic mirrors.

quack
Message: Posted by: RangeCowboy (Jul 10, 2002 02:29PM)
My ten cents,

The perspex/plastic mirrors are thinner and lighter than glass and almost indestructible. You can buy remnant pieces 3 or 4 feet sized on eBay. If you buy a large section you may need to stick wooden stiffener behind it or it may bow or convex in operation which is quite noticeable.

My biggest complaint with ANY rear-surfaced mirror is that when using multiple mirrors together the light tranmission is reduced dramatically and so you must be careful with lighting. I believe the old stage illusions used surface plating of nickel on steel for durability and almost 100% reflection but at an immense cost and weight.