Would it be possible to to take, say, Anderson windows and rapidly pump opaque liquid into the space between the windows to create a window without a view? It would save on shades!
It seems to me that making the window opaque wouldn’t be as difficult as making it transparent again. You’d have to find a liquid that didn’t adhere to the glass at all or it would leave drops and streaks as it was withdrawn.
Also, from an economic standpoint it’s pretty hard to beat hanging cloth. I know you can spend a lot on drapes but the mechanism is relatively simple compared to what it would take to pump liquid into and draw it out from between two sheets of glass. And the liquid itself would have to have some special properties – in order to be opaque in a relatively thin layer it would need to have a lot of pigment or something similar in it. Most liquids that aren’t tap water are pretty pricey!
So pipe down and draw the blinds. The sun’s shining in my eyes.
The basic concept has already been done, though not the way you suggested. Instead it is done using ion-storage materials that change electronically from transparent to opaque.
I can’t find a more recent link talking about production windows using the technology, but here is one that at least explains how it works.
A better way is to make window panes out of LCD displays. Have you ever seen one of those transparent plastic desk clocks, with the big black LCD numbers? The LCD display is embedded in the plastic. It turns opaque when a certain voltage is applied, and clear when it’s removed. You can already get window panes like this, and by rapidly changing the applied voltage, you can vary the transparency.
I haven’t heard about them in a while, but they were at least $100 (US) per window pane several years ago.
Arjuna34
Is LCD really better than the ion storage technology? I agree it a proven technology that works well enough, but it’s not cheap, and needs a constant power source. Another problem with LCD is that even in the transparent state, it only transmits half the light. This is because LCDs are made of two polarizing filters with a liquid crystal layer in between. Light passes through the first filter and is linearly polarized, then the liquid crystal alters the polarization depending on the voltage applied, controlling whether it can or cannot pass through the second polarizer filter. No matter how you design it, the first polarizer absorbs half the light. It sounds like the ion storage device does not have this limitation.
My first simulpost! I didn’t see the post about the ion-storage windows- sounds pretty cool! Yes, LCD windows only transmit half the light at “full” transparency, so you wouldn’t get the full effect of having sunbeams shining into your house. The power needed to run an LCD window is very small, so I don’t think that’d be an issue. The ion windows sounds much better, though.
I’m pretty happy with my venetian blinds 
Arjuna34
So how 'bout two round windows of polarized glass? Set the outer one in place so it’s immobile, and the other one on a track, either manipulated manually or by wheels drawing on a power source. Rotate it 90 degrees and you’ve got shade or light, depending on the position. 'Course that depends on the cost of polarized glass but it seems cheaper than an LED, at least at first glance.
I recall seeing an article (many years ago) about fluid-filled windows that were even simpler than drapes. One pane was flat, the other angled on the inner surface. A glass wedge could be pushed between them to displace the fluid to a reservoir, or withdrawn to let the opaque fluid flow between the panes.
Of course, the fit-and-finish required would still be expensive, and a window like that would still make a real mess if it cracked.
I’ll stick to drapes for now.
I had understood that the ion-storage windows used polarization, too, though I could be mistaken. Also, it takes the next best thing to no energy to maintain an LCD-- most of the energy is involved in changing the state. In any event, while such things may have specialized applications, in general they’re going to be a lot more expensive than the old-fashioned curtains or blinds.