There are different grades of silica gel - non-indicating (white)
and three self-indicating types (orange to green, orange to colorless and blue to pink).
There are two physical forms of the silica gels,
bead (more uniform spherical) or granular (irregular crystals),
which are further sub-classified by the diameter of their particles.
Non-indicating (white) silica gels
2 - 5 mm and 1 - 3 mm bead
0.2 - 0.5 mm, 0.5 - 1.0 mm and 3 - 6 mm granular
Standard white, non-indicating silica gels offer the highest weight for weight moisture adsorption capacity.
Self-indicating silica gels
Orange to dark green
2 - 5 mm and 4 - 8 mm bead
0.5 - 1.0 mm granular
Using an organic indicator this silica gel offers a very strong orange (dry) to dark green (near exhausted) color change.
Mostly used in the low dusting, beaded forms.
Orange to colorless
2 - 5 mm bead
1 - 3 mm and 3 - 6 mm granular
Using iron salts as the additive, this high-capacity desiccant changes from a deep orange (dry) to a very pale-yellow color
in an exhausted state. The indicator is very robust, making this silica gel well suited to repeated regeneration and reuse.
Available in both granular and beaded physical forms.
Both orange self-indicating silica gels are non-toxic materials developed following
the reclassification of blue to pink self-indicating silica gel as a toxic material in the year 2000.
Blue to pink
2 - 5 mm bead
0.5 - 1.0 mm and 3 - 6 mm granular
Changing from blue (dry) to pink in its near-exhausted state and still popular in many regions and industries,
it is the cobalt in the cobalt chloride indicator that is responsible
for the toxic labelling and disposal restrictions on this grade of silica gel.
It still though remains, not regulated as dangerous goods for transportation purposes.
All self-indicating silica gels are sold in bulk or can be packed into sachets.