How do I determine if something is crystal or just glass?

Question

this is in regards to prisms for an antique lamp. We cannot tell if they are glass or crystal

Answer 1

The correct way to identify whether a material is crystal or glass is to use an X-ray diffraction technique as pioneered by Bragg or Laue. The wavelength of x-rays are typically around 1 angstrom (10^-10 metres) this is comparable to the interatomic spacing in a solid. So by performing an optical diffraction experiment is it possible to deduce the spacing of the planes within a crystal, and thus determine the size of the unit cell. Furthermore from the reflected intensities of the diffracted beams we can obtain information on the arrangement of the atoms within this cell. It is easy to prove Bragg's law (see any good solid state physics book): 2dsin(theta) = n(lambda) where d is the distance of the atomic planes, theta is the angle of the incident radiation with respect to the horizontal plane, n is the order of the diffraction (n=1 is 1st order diffraction number) and lambda is the wavelength of the incident radiation.

What happens when this experiment is performed over many different planes on the crystal of interest is that we build up a series of data which tells us the crystal type. I shall not go into the detail of this (again you need to look this up). What you find is that crystal structures display specific patterns when x-rays are diffracted. This is because they have a periodic structure and it turns out that this periodicity causes larger intensities in the diffraction pattern at certain angles. Glass does not have a periodic atomic sequence (it is completely random) so it will not have any particular diffraction pattern (i.e. it will look like a mess).

Having just read the 2nd part of your question (with regards to an antique lamp) then this technique is perhaps not so useful to you. So as a rule of thumb I think you should look to see whether your lamp is smooth or rough. If it is smooth it is probably glass; if it is jagged then it is likely to be crystal. Glass is difficult to make into a regular jagged structure. As a crystal naturally has a periodic structure it can form regular jagged edges and still remain strong.

Answer 2

Crystal has a higher index of refraction than glass, because it has a periodic molecular structure.

If you shine a laser through it, it should bend the beam more than if you shined it through a equal thickness piece of glass.

If you have a high powered microscope you maybe able to tell by examining the structure of the lamp. Crystal should have a more organized and periodic structure.

Answer 3

You then need to perform a simple experiment. At first take that thing beside a window, make sunlight pass through that thing. after the ray of light has passed through it, if the shadow which falls on the wall is of 7 colors (spectrum) then it is a crystal and if not it is a glass. Naf :-)

Answer 4

Leerdam, near Rotterdam in the Netherlands, has been a site of glass making since the 18th Century. In 1878 an existing bottle plant was extended with a glass works for table glasses, both blown and pressed. During the first years of production, the designs were anonymous, and followed the tradition of drinking glasses elsewhere. Decanters, stemware, counter jars and similar articles were decorated with etched, engraved and cut designs and the resulting production was so traditional that it could have been produced almost anywhere. The same is true for pressed glass patterns, which are completely in line with the taste of the period. These products were not just for local distribution, but were also exported to England, South America and Mexico.

During the great age of glass innovation at the turn of the century, Leerdam kept out of the art glass market. At the time there was an important idealistic movement to improve the quality of everyday design, led by architects and furniture makers. Shapes inspired by nature were stylised, geometrical designs introduced and the role of ornament was reduced. This Functionalist movement, which was inspired by the Arts & Crafts movement in England, was led in the Netherlands by the architect Hendrik P.Berlage. He believed that architects should not limit themselves to designing buildings, but that they should also tackle decoration, furniture and tableware. His first designs for vases and stemware date from 1900 - but it would be 20 years before the Leerdam glass factory actually produced any of his designs.

In 1915, the first glass designs were commissioned by P.M.Cochius, director of Leerdam Glassworks, from the architect Karel P.C.de Bazel. Around the same time, Cochius commissioned glass designs from other famous architect-designers such as Cornelis De Lorm, Chris Lanooy, Chris Lebeau, and Hendrik P.Berlage and from the young factory designer Andries Copier (pronounce koh-peer).

Answer 5

Jewelers have a "hardness" device which can tell the difference between a quartz stone and a glass crystal. You can also take the stone to an auction house which carries jewelery and they can determine it for you for free.

Answer 6

Compounds are added to glass to alter its physical or optical properties. Boron for heat resistance, sodium for better flow when pressing bottles, flint for optical properties, cobalt for blue, gold for red, and lead oxide (in fairly large amounts) to increase the index of refraction somewhat dramatically. This gives lead crystal its brilliance. So lead crystal can be identified either by its density (or specific gravity) compared to another glass, or by its higher index of refraction. If you can measure one of these properties, you can identify it. You can also purchase a lead detecting chemical test--if it shows lead is present, it was deliberately added to the glass for brilliance. That's assuming you can swab enough lead off the surface for the test to work. It's worth a try because I think you can.

Answer 7

im not sure if this helps, but when it comes to things like wine glasses, generally you should be able to "feel" the difference, i.e the one made of glass will feel "cheaper" and (as mentioned) lighter than a crystal one of similar size. Don't know how this would relate to your querie tho.

Answer 8

Tap it with your fingernail. If it has a clear longish sound it is crystal. If it glass,it is just a dull thud.

Answer 9

you must know what is glass & what is crystal, as we can see glass cannot form a lattice, that is its molecules are disordered & rigidly bonded. on the other hand crystal's molecules are ordered & can form regular lattice. so i must say you will see a complete difference between crystals & glass.

this is the simple way to understand them, look which one is more crystalline. the non crystalline must be the glass.

there's more way to find which one is glass & which one is crystal...

here's some links...

Answer 10

Crystal weighs alot more, because it has lead in it. Really besides the weight I don't know.