I'm not going to give any directions about where to find the various commands that you will need to use, because I don't know which application you are using, and the basic principals hold true no matter which one is your favorite.
You will need to know where to find the various attributes in your own software, however. If you don't, I suggest that you look in the owner's manual. (Or you could just poke around in the menus until you see them! <g>)
There are three things the control the actual transparency that you will see in your finished render.
The first, of course, is the opacity of the shader itself. This is usually set with a slider, and will be labeled something like "Transparency" or "Opacity." Normally, it's expressed as a percentage. It's use should be clear, if you'll pardon the pun.
The second is the amount of diffuse and/or ambient light the shader will accept. Once again, you can normally find this right in the shader dialog, as a percentage slider. The more light your object will accept, the cloudier it will appear. The less light, the cleaner it will seem.
The third, and perhaps most important setting is the amount of transparency recursion in the render. This is generally hidden in an "expert settings" dialog box someplace. Basically, it lets you choose how many levels of things are transparent before the renderer stops trying to look through things, and either just gives them their base color or makes them black, depending on the application. Each time a light ray goes through something, that counts as one level. So a glass bottle, like this one, would have one for the front of the first wall, and one for the back of that wall. Then it would have another for the front of the back, and one for the back. So if you want to see the whole way through the glass, you need at least 4 levels of transparency.
Reflectivity recursion is a related value, probably found in the same place, which determines how many times the renderer tries to follow a reflection before it gives up. In the examples below, the bell is reflected in the bottle. But that reflection has a reflection of the bottle in the bell, and so on, bouncing back and forth.
In your renderings, look specifically at the shadows. If there seem to be opaque shadows from things you wanted to be transparent, I suggest that you increase these values.
With both of these, the more you have the more realistic your rendering will be (in the real, analog world light never does give up!) But also the longer it will take to render. And there is a point of diminishing returns where you have see through the bottle, or the reflections get to small to be visible anyway! So my advice is not to overdo it here. Count it out, have fun, and get the render done!
If you have a question, write to me and ask it!
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