Masking Transparent Objects

Open up your image in Photoshop, then take the pen tool and start drawing around the object you want to make transparent.
When you have masked the whole object, right-click and then select “make selection”. feather should be 0, then go ahead and click OK.
When you have a selection, press CTRL + C and then CTRL + V, to create a new layer with your object. Hold down CTRL again and then press on your new layer icon in the layers tablet, to make a selection. With that layer selected, go up to “Edit” and click on “Copy Merged”.

Go to “Channels” and create a new channel (the background should be black), then press CTRL + V, to paste. With you new channel selected, go to “Image”  “Adjustments”  “Levels”, and adjust the levels so your object looks something like the bottle below. Then press the CTRL and press the channel layer, this will make a selection that looks a little weird, do not worry about it.

Make the RGB channel visible again, and then go back to “Layers”. Create a new layer, go up to “Edit” -> “Fill”, and for contents use White. Click OK. You can now see the transparency, and you may deselect your selection.

Now, load up a picture that you want in the background, or inside your object. Put it underneath both of your previous layers (as below). Make all of your layers visible at this time, background, original object, and your transparent object. Press CTRL and click on your original object layer to load its transparency, make sure that your object is marked and that your background layer is selected. Go to “Filter” –> “Blur” -> ”Gaussian Blur”, and blur your background a little. If you cannot see your background through your object, just lower the opacity on your original object.

Here’s my finished transparent water bottle, you can duplicate your transparent layer to get a better effect, and play around with the opacity of the original layer.