So! In 40d it was perfectly possible to tan the chitin of giant cave spiders or whatnot, yet it isn't in 2010. So I added it.
Update; I also made it into a SHELL material.
If you haven't touched material_template_default or b_detail_plan_default, you can download the relevant raws
here. Otherwise, you will need to install it manually by doing the following:
Stick this material definition into material_template_default, down the bottom.
[MATERIAL_TEMPLATE:TANNED_CHITIN_TEMPLATE]
[STATE_COLOR:ALL_SOLID:GRAY]
[STATE_NAME:ALL_SOLID:treated chitin]
[STATE_ADJ:ALL_SOLID:treated chitin]
[STATE_COLOR:LIQUID:GRAY]
[STATE_NAME:LIQUID:n/a]
[STATE_ADJ:LIQUID:n/a]
[STATE_COLOR:GAS:GRAY]
[STATE_NAME:GAS:n/a]
[STATE_ADJ:GAS:n/a]
[DISPLAY_COLOR:7:0:0]
[MATERIAL_VALUE:1]
[SPEC_HEAT:420]
[IGNITE_POINT:10508]
[MELTING_POINT:NONE]
[BOILING_POINT:NONE]
[HEATDAM_POINT:10250]
[COLDDAM_POINT:9900]
[MAT_FIXED_TEMP:NONE]
[SOLID_DENSITY:500]
[LIQUID_DENSITY:NONE]
[MOLAR_MASS:NONE]
[IMPACT_YIELD:10000]
[IMPACT_FRACTURE:10000]
[IMPACT_ELASTICITY:100]
[COMPRESSIVE_YIELD:10000]
[COMPRESSIVE_FRACTURE:10000]
[COMPRESSIVE_ELASTICITY:100]
[TENSILE_YIELD:10000]
[TENSILE_FRACTURE:10000]
[TENSILE_ELASTICITY:100]
[TORSION_YIELD:10000]
[TORSION_FRACTURE:10000]
[TORSION_ELASTICITY:100]
[SHEAR_YIELD:115000]
[SHEAR_FRACTURE:130000]
[SHEAR_ELASTICITY:100]
[BENDING_YIELD:10000]
[BENDING_FRACTURE:10000]
[BENDING_ELASTICITY:100]
[MAX_EDGE:1000]
[ABSORPTION:100]
[IMPLIES_ANIMAL_KILL]
[LEATHER]
[ITEMS_LEATHER]
Now add these lines to CHITIN_TEMPLATE in the same file.
[SHELL]
[ITEMS_HARD]
[ITEMS_SCALED]
[MATERIAL_REACTION_PRODUCT:TAN_MAT:LOCAL_CREATURE_MAT:TANNED_CHITIN]
Finally, add the following line to the CHITIN_MATERIALS body detail plan in b_detail_plan_default.txt.
[ADD_MATERIAL:TANNED_CHITIN:TANNED_CHITIN_TEMPLATE]
Currently, it's exactly the same as leather, but you can modify the values like you would with any other material. Please comment if you have any trouble, as the manual installation may be a bit tricky.