first of all model a glass - duh. since glass is extremely bitchy in sl please make sure that you have enough space between the inside and the outside of the glass. Oh and each and every glass needs an inside and an outside!

I work with HDRI maps (highly recommended) but since glass is super reflective so called fireflies can and will happen. There is a way in avoiding them...

you can find other ways dealing with fireflies in this article here: 7 Ways to Get Rid of Fireflies Once and For All

now comes the material. Making glass in blender is fairly simple - just use a glass shader and you have a jolly good render of a glass. Sadly this does not translate to the texture, because...

...you will end up with a complete solid texture with absolutely zero transparency. This is what we are going to fix in a second in Photoshop. I am not that familiar with GIMP but I am sure there are similar ways to archive what we are doing.

we are in Photoshop - and no surprises - the texture indeed ist full opaque. meh

copy the layer and reduce the saturation (making it black and white). Use brightness and contrast (brighten it up a bit and turning contrast down low)

use again the brightness/contrast command - this time leave brightness but again lower the contrast

select the whole layer and copy it (ctrl+c)

now switch from the Layer Tab to the Channel Tab. Create a new channel. By default this channel is black and is called "Alpha1". Sounds good, cause "alpha" smells like this has something to do with transparency

now paste the image you copied in the alpha channel. You will have now a black and white gradient picture of your glass texture in your channel - the same one we just created. And this is good!

click on this circular icon (far left on the bottom of the channel tab) and you will get "marching ants" all over your texture. This command selects all white areas (and also gradients from white to black), making white full opaque and black full transparent (and everything inbetween - erm - inbetween)

now go back to your Layer Tab and select the bottom layer - the one with your baked and not manipulated texture on it. Copy and Paste (ctrl+c, ctrl+v) the selection. A new layer appears above your texture. Let's have a look at this layer:

this looks fairly good. The texture is not opaque anymore but has parts that are opaque and parts that blend into transparncy. Nearly perfect! You can lower the layer opacity in general if you still have some solid white spots. Also - depending on your HDRI map - you can brighten up the texture. Even if it maybe looks like...

...you do not change anything about the transparencies with brighten the texture up.

save your semitransparent texture as PNG and choose as save option "no interlace". BTW: It is glass - so just transparency and reflections. You do not need to safe it as 1024x1024 texture - 512x512 or even 228x228 is big enough!

This was the main part on the glass texture - you can use the created PNG texture as glass texture for your mesh but also as Specular map for your mesh. If you have a quite colorful HDRI-Map i recommend to reduce saturation for the SPEC map.

We are going back to blender. Remember that i said that glass needs an inside and an outside? Now comes the rather tricky part: Due to the rendering of SL the glass needs different materials for the inside and for the outside. Here blue and red. Assign these materials before you export!

It gets more tricky: If you are doing your LOD levels you MUST make sure that in every LOD version there is AT LEAST one tris for each material you have assigned. Otherwise the mesh uploader will refuse to upload your model. If you keep this in mind you are fine and good to go.

And that's about it. This is how I do glass and so far it worked quite good. Hope that helps

runatsurine: I do not think that there is a possibility to bake glass textures with transparencies since the glass shader (i believe in every program) is mainly for internal rendering and not for texture work in whatever environment. I might be wrong on this one and if there is an easier way i would LOVE to know it

Oh but that brings me to another point: If you are doing glass render it solo and NOT in a scene. Reflections of other things (tables, shelfes and such) will be in the texture and give out false transparencies. And also the glass will be damned in sl to stay at exact the same spot like you put it in blender - otherwise it will look dodgy

you can compare it to baked in shadows. The only situation I can think of glass reflecting another object is when it is connected to something else - like in a lamp i.e.

but usually i always would recommend to bake glass seperated from everything else

that's so useful, even tho I do not use Blender for my glass right now I'm gonna give it try soon :3

let's all love paco 'v' ZeeZuleicca PixieRuby

runatsurine: i've baked glass alphas in blender. DON'T. it takes forever and ever and ever and still ain't that great. you basically get what you've got there, but the added bonus of waiting 10 hours for it.

This works with the mia_material glass presets in Maya as well.