RUBY ROUGH

Birthstone for  July

This is a natural rough Ruby which has been  treated  and  showing stunning colours of red with a purple tinge.This specimen can be cut into a large stone or it is ideal as a carving piece. We have placed the rough under a bright torch to do the photos.The rough is more opaque than transparent.

This is a piece of rough mined in Madagascar-africa.The material has been heated to improve its colour and it has also been treated by lead glass filling

Mohs scale 9

A Ruby is a pink to blood-red gemstone  a variety of the mineral corundum (aluminium oxide]. The common red color is caused mainly by the presence of the element chromium. Its name comes from ruber, Latin for red. Other varieties of gem-quality corundum are called sapphires. Prices of rubies are primarily determined by color. The brightest and best “red” called pigeon blood-red, commands a huge premium over other rubies of similar quality. After color follows clarity: similar to diamonds, a clear stone will command a premium, but a ruby without any needle-like rutile inclusions will indicate that the stone has been treated one way or another. Cut and carat (size) also determine the price

TREATMENTS

The most common treatment is the application of heat. Most if not all rubies at the lower end of the market are heat treated on the rough stones to improve color, remove purple tinge, blue patches and silk. These heat treatments typically occur around temperatures of 1800°C (3300°F).Some rubies undergo a process of low tube heat, when the stone is heated over charcoal of a temperature of about 1300°C (2400°F) for 20 to 30 minutes. The silk is only partially broken as the color is improved.

LEAD GLASS TREATMENT 

Filling the fractures inside the ruby with lead glass dramatically improves the transparency of the stone, making previously unsuitable rubies fit for applications in jewelry. The process is done in four steps:

1. The rough stones are pre-polished to eradicate all surface impurities that may affect the process
2. The rough is cleaned with hydrogen fluoride
3. The first heating process during which no fillers are added. The heating process eradicates impurities inside the fractures. Although this can be done at temperatures up to 1400°C (2500°F) it most likely occurs at a temperature of around 900°C (1600°F) since the rutile silk is still intact
4. The second heating process in an electrical oven with different chemical additives. Different solutions and mixes have shown to be successful, however mostly lead-containing glass-powder is used at present. The ruby is dipped into oils, then covered with powder, embedded on a tile and placed in the oven where it is heated at around 900°C (1600°F) for one hour in an oxidizing atmosphere. The orange colored powder transforms upon heating into a transparent to yellow-colored paste, which fills all fractures. After cooling the color of the paste is fully transparent, that dramatically improves the overall transparency of the ruby.