Bellingham + Stanley Ltd. E-Line Instruction Manual

Gemological Refractometer
Eyepiece Body
Prism
Torch Filter

Specification

Measuring range
Minimum graduation value
Size
Weight
Order Code
44-861
Bellingham + Stanley Ltd.
Longfield Road, Tunbridge Wells, Kent TN2 3EY, United Kingdom.
Telephone: +44 (0) 1892 500400 Fax: +44 (0) 1892 543115
Website:
44-895 Iss 01 Rev 0
E-Line Gemological Refractometer
Upper
Cover
Polariser
Light Entrance
Socket
1.30-1.81
0.01
30x70x130mm
400g
Description
E-Line Gemological
Refractometer
www.bellinghamandstanley.com
Instruction Manual
Refractive Index is one of the most important optical parameters used to
identify and authenticate polished precious and semi-precious gemstones. The
E-Line Gemological refractometer is a low cost, lightweight measuring
instrument used by jewellers and traders of gemstones. The Gemological
refractometer can also be used to identify whether a particular stone is
Isotropic or Anistropic (uniaxial or biaxial).

Method of Operation (Singly Refractive)

1. Place the instrument on a suitable table. Open the upper cover. Drop a
few drops of contact liquid (see table over page) onto the surface of the
prism using a thin glass bar or soft wooden stick. (
Liquid - Read Material Safety Data Sheet
2. Gently place the polished surface of gemstone on the prism, depressing it
lightly to make sure contact liquid is distributed evenly between the
gemstone and measuring prism.
3. Close the upper cover.
4. Place the light source in the light entrance socket of refractometer.
5. Look through the eyepiece and by a push/pull action; focus so that the
light/dark demarcation line can be seen in the field of view against the
refractive index scale.
6. Read the refractive index of the gemstone from the scale where the
demarcation line crosses the refractive index scale.

Anistropic Gemstones (Doubly Refractive)

Anistropic gemstones will display two demarcation lines when viewed through
the eyepiece. These stones are sometimes known as 'bi-fringent' or 'doubly
refractive.' There are two types of Anistropic gemstones: (1) uniaxial, which
has a single optical axis that does not cause light to doubly refract, and (2)
biaxial, which has two optical axes that do not cause the light to doubly
refract.
It is possible to identify whether a stone is uniaxial or biaxial by using the
polaiser and/or by rotating the gemstone through steps of 90°, taking
6
refractive index measurements and monitoring the movement or prominence
of the demarcation lines. Simple differentiation between uniaxial gemstones
and biaxial gemstones can easily be achieved by rotating either the polariser or
gemstone, where one demarcation line will remain static (uniaxial) as opposed
to both demarcation lines varying in position (biaxial). More complex
determination can be achieved by measuring the angle of double refraction as
detailed below:

Using the polariser to identify Anistropic Gemstones

1. Place the gemstone on the refractometer following the steps above.
2. Place the polariser on the eyepiece.
3. Turn the polariser in the eyepiece until a single borderline is seen (light is
vibrating in one direction only, eliminating the extra-ordinary rays caused
by birefringence).
4. Read the refractive index.
5. Gently rotate the gemstone on the prism by 90° taking care not to scratch
the prism.
6. Turn the polariser by 90°
7. Measure the refractive index of the light vibrating at 90° to the
measurement in point 4.
8. Repeat steps 5 to 7 until the stone has passed through 180°
Interpretation of the results will identify the value of double refraction by
calculating the difference between the measurement group with the maximum
refractive index and the measurement group with the lowest refractive index
and comparing to known data.
Email: sales@bellinghamandstanley.co.uk
CAUTION: Contact
).