Good Glass

What to check for in assessing if the glass your buying is of the highest quality?

To put it simply you have to check for the 4 C’s

  • Clarity
  • Colour
  • Cutting
  • Consistency

Clarity – by the very nature of glass – its appeal through its harmony with light – allows for interesting and creative uses both in the interiors and exteriors of any building and visual clarity is of paramount importance for glass for such usage. It may sound very odd but one should never be able to see good glass, for it should be virtually invisible.

What factors affect the clarity of the glass?

  • Surface defects like scratches, tin defects etc
  • Thickness variation
  • Absence of parallel surfaces (face and underside)
  • Undulating surfaces
  • Body defects inside the glass like bubbles, stones etc
  • Body defects due to inhomogeneous glass composition like reams, chords etc

Colour – ‘Body tinted glass’ is produced by adding exact quantities of metal oxides at the time of float glass processing in the Furnace. This brings about a change in the colour of the glass, without affecting the basic properties of the glass itself.

An important need is for a clear glass that is without colour. This is difficult, because of impurities (like iron oxides) in the glass, which are difficult to remove. Depending upon the amount of iron oxides and the relative concentration of ferrous oxide to ferric oxide (a factor called redox), clear glass trends to have a greenish/bluish tinge. This greenish/bluish tinge is more prominent when the glass is seen edge-on.

Since manufacturing exact shades of tinted glass is extremely difficult and requires precise computerized control, in purchasing tinted glass one has to ensure that a branded high quality supplier is chosen – since if any breakage occurs after a couple of years the exact ‘tint’ might not be available.

In tinted glass, precision in colour depends on manufacturing skill. There can be possible variations in colour from batch to batch and the challenge in manufacturing tinted glass is to achieve the exact colour in every production run. This can be achieved only if there is an accurate specification and measurement of the colour of glass in mathematical terms called colouristic values which interpret any colour in a three dimensional format on the axes of hue, chroma and brightness.

Cutting – Glass has to be cut to different shapes and sizes depending on the requirements of the customer. And in all these processes, the ‘cut-ability’ of glass is very important. This means that the glass should break cleanly along the score instead of breaking in a irregular way – This is difficult to do if the glass is of poor quality.

Some other cutting problems are:

  • Newly cut edge being slanted. This means more time spent on grinding, polishing and beveling of edges.
  • Edge of the newly cut glass having hackles
  • Problems in cutting of thicker glass
  • Chipping from the cut edges

What makes glass difficult to cut?

Uneven stresses can form in the glass during cooling of the molten glass. Uneven internal stress happens when annealing is uneven. This leads to stress variation across the width and the thickness of the glass. This in turn leads to difficulty in cutting, beveling and working with the glass.

Consistency – It means consistency in colour -which needs to be the same over years so that when broken glass is replaced in a building, there are no colour variations. It also means consistency in length, width and diagonal. Most importantly, it is also consistency in thickness.

  • The glass sheet may not be perfectly rectangular. This means fixing and fitting of the sheet becomes a problem without corrective edge grinding that adds to cost.
  • The glass sheet may not be of consistent thickness. This leads to problems in cutting, beveling and channel fitting.

Contact us if you have any questions regarding the above – and want to purchase best quality glass.