Hi Sepp,

I don’t think you need the density parameter since the GCOS uses the relative cost and this is already an approximation, so the benefit of converting from weight to volume might not be worth it (lower GCOS/volume might be more difficult to work with so you will need to contact your manufacturer to determine the manufacturing cost for a given material).

If you want to get the density, you can use TMAS to get the mass, VOLU to get the volume and then PROD/PROB to do unit conversions to get the relative cost per volume (both TMAS and VOLU use centimeters regardless of lens units). 

Also, if you really need to dig down into the raw material volume, you will have to calculate the blank volume using BLTH and DMVA.

Thanks for the helpfull answer.
I know that the GCOS  is only an apprximation, but at least the approximation is getting better if I consider the real mass of the lens or as you say the blank volume.
A great thing would be, if we also could considder machinability of the material. My former boss tried to make a classification for Schott and Ohara glass 30 years ago, but I think there is nothing available in the community?
 

@Sepp Can you describe more about how you measure/quantify machinability of a material? 

Hi Alissa,
at my first company 35 years ago, we have got an additional list from fabrication about following properties in an in-house list:

• stability of AR coating
• high thermal expansion (this is already in your tables)
• long polishing time
• glass may be “bedded” (I hope I found the right english wording)
• glas is not sutable for prism
• glas tend to have blur after polishing