Projection onto glass building: thoughts and suggestions please

  • Hello Isadora community, I'm looking for guidance. I'm involved in a project to illuminate a large building with video content. The building is primarily glass fronted.

    My question is if we project imagery onto glass will it be visible? We have no experience of this so I'm looking to this community for their own experiences. Please can you advise me on whether we need to treat the glass with a film to ensure the content is vivid, do we project from the front as if we were projecting on to a surface on a stage or do we rear-project onto the glass? We've got budget for several projectors in the 20,000 lumen range. 

    Thank you for your time and help.


  • glass will reflect some, and be invisible to most of the projected light unless treated. it may be better to back-project onto some kind of screen material that is stretched across the window, depending on what kind of space you have behind the windows.

  • If you are doing a frontal projection with a 20k (in the dark) and the building is dirty/dusty enough you might get a decent image, there is no way around making a test though. 

    I would also try doubling 20ks if you need more punch.

    Ps. Make sure they don't clean the windows between now and your show

  • @dbini @fubbi Thanks both for your input. The building in question is still being constructed and so the glass is most likely very dirty at the moment but come the event windows may have been cleaned, that's out of my control. Maybe I will look at rear projection the rooms are large and projectors can be set well back. Would anyone have suggestions or could they share their experiences of using a film to cover the glass and where I may purchase such material. One question I have is can can the film be removed easily, does it leave any marks? Thanks again!

  • Screen material choice will depend on how large your windows are and how far away your audience is. 

    I've used various things in windows to back project onto. Rosco RP screen is awesome, but very expensive. there are various films that you can apply directly to the window but these will need to fit exactly, otherwise you get bright lines appearing on the edges. If your window is higher than the audience and you project from the floor of the room then you don't get that nasty back-projection hotspot issue, so you can get away with using cheaper screen materials - I tend to use basic cotton sheeting stretched on frames and clamped to the window frames, but then I always seem to be working to a tight budget. I built an RP screen using a lightweight rubbery material - I think it was the kind of stuff that hospitals use to protect mattresses. That worked really well. 

    I discovered two issues last year when projecting onto window screens in different rooms - I had 6 projectors over 2 floors - that the projectors need to be the same, with similar lamp life, and with a bit of luck they will output something similar. And that you need a solid solution for mapping. from inside the building I couldn't see the whole image so I needed somebody outside on the phone to guide me with tweaking the map, even though I had designed the content to be as simple as possible and to compensate for the difficulties of the building.

    Fubbi's idea of blasting as many lumens as you can find onto dirty glass is a good solution if you have the right place to project from. 

  • @paz

    I often used buttermilk to paint windows with it. It really works very well with a little practice. Just paint it like a wall with a painting roll. But the one with foam.

    The result depends a bit on the rolls and the thickness of the buttermilk. You can try to mix it down with water a bit.

    Realy, I'm not joking! And no, it won't smell as it dries very fast! Easy to remove with water. Very cheap, but very nice result like frosted glass (Actualy in German it is called Milchglass = milk glass ;-) ).

    Best projecting result would be to project to the painted site of the glass, but depending on the glasses thickness, it might work from the other site.


  • @paz

    here is an example where we worked with the buttermilk.

    Watch the video, and pay attention to the upper parts of the windows, where the text is projected on. It is the exact same glass, that was used for the lower main window!
    There are some pictures in between the text as well.

  • @DillTheKraut I use buttermilch too. Its 100% a good idea, but it should be mentioned that there is a small stink phase involved as it dries and dies.

    If you want to spend money there are films from Gerriets, 3M and even on amazon these days:

  • Hey thank you so much @dbini @DillTheKraut @fubbi for your thoughts and ideas. I have time to experiment as the event is not until October. I will let you know how I get on!

    Thanks once again and best wishes, Paz

  • @fubbi

    Hmm, strange. Never had that smelling, beside the natural buttermilk smell. Maybe it's the branch, wich one are you using? 😄

  • .. there's also a product that is used for painting onto glasshouses when it gets too hot for the plants inside. Its called shade compound or Coolglass. Its a white solution that you dilute with water before applying. It definitely doesn't smell and washes off easily. it might be worth experimenting with that and a roller...

  • Beta Platinum

    sounds like great project and agreeing with all the suggestions

    A few other thoughts: ** experiment a LOT with the refraction / reflection angles. Probably some of my favorite work has been complex reflections off the glass onto the other surfaces from really unusual angles.

    * Two other unusual films that I've had interesting results with : polifilm (various brand names) - makes the blue or green or clear film that's often on new windows; and the other cheaper alternative are various brands of tinted pallet wrap 

    * and - I've found that the tinted IR /UV coatings on many new commercial windows (at least in California) are just enough tint to let a ghost image condense.

    * and finally - a uniform mist on glass makes a fabulous ghost projection surface...

  • Just quickly wanted to add a big thanks to @Ian and @dbini for the additional ideas and product info!

  • Beta Gold

    That buttermilk suggestion could saved me a lot of money..... Thanks for the tip! I will try in the future.