From Wikipedia:
Technical week (also called tech week or production week) refers to the week prior to the opening night of a play, musical or similar production in which all of the technical elements (such as costumes, lights, sound, and makeup) are present during rehearsal for the first time.
Prior to this point, the actors may have been rehearsing in a separate rehearsal hall, or on the stage but without all technical elements present. At this point in the rehearsal process, it is expected that the creative aspects of the production are ready. Actors have their lines memorized; lights, sound, scenery, and costumes have been designed and completely constructed. If the production is a musical, then the orchestra has rehearsed the music completely, and any dancers are prepared with their choreography memorized. During technical week all of the various technical elements are fully implemented, making the rehearsals very similar to the actual performance.
The purpose of tech week is to rehearse the show with all technical elements in place. This allows the actors to become familiar with the set and costumes, the technical production crew to iron out unforeseen problems, and the director to see how everything comes together as an artistic whole. Tech week is when practical problems with the implementation of production elements are discovered. For example, an actor may report that their costume restricts their movement or that a hand prop is overly cumbersome. A set door that performed fine the week before may bang shut too loudly now that there are live microphones on the stage.
Rehearsals during technical week generally start just after lunch and often run until midnight or later. The first few rehearsals are characterized by the frequent stopping and starting of scenes so that the technical crew can practice their necessary duties (such as executing their cues or scene changes correctly). That the director will make major changes to various artistic elements during technical week is the rule, rather than the exception. Everything that goes wrong during a rehearsal is expected to be fixed by the next day.
The repetition and the long hours make tech week boring and tiring for the actors. For the technicians, it is the most hectic part of a show's run, as they are forced to do a massive amount of work getting timings and cues correct, often without having seen the scenes in their entirety. Tech week is a very stressful time for all involved in a production. As the week wears on, sleep deprivation increases and tempers often wear thin.
Once the show is running smoothly, the last one or two rehearsals of technical week are often dress
rehearsals open to the public in which the play is performed completely, sometimes with the audience purchasing discounted tickets.
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This is one of the most exciting stages of creating a piece of theatre: watching everyone's weeks and months of hard work come together over a week of twelve to fifteen hour days to create the three hour musical you see when you come to the theatre.
The crew and stage management team will show up around 8am (if not earlier) to set up all of the props, furniture and set pieces they have already collected from the property designer and creator the night before. They create a stage right and stage left prop table (or in our case, a props shelf), complete with labels detailing every single prop and it's location. The crew has already been building the set for over three days.
Around the same time, the Wardrobe department receive the costumes from Angels, the costume builders, and label and deliver every costume to the designated dressing rooms. They prepare to iron, sew and alter and discard as needed throughout the day.
The lighting team has set up their lighting board and has begun to assess the set and what lights are available, and they begin work immediately. In this particular production, there was a real challenge with lighting due to the projections.
The sound team are setting up the sound board, testing and setting up the speakers, the fold-back, the orchestra mics, and then labeling and distributing company microphones, colouring mic cords, preparing hair clips and elastics.
The cast arrive at 10, and get in to costume, microphones, make up and hair, ready to begin from the top of the show at 11. (In our particular instance, the orchestra did not arrive until the second day for the Sitzprobe, because the prologue takes the entire first day of tech, which we do with a rehearsal piano.)
We then take the show, moment by moment, detailing every single technical aspect until it is just right, only moving on when we are all happy with it. There is tremendous pressure to do it quickly, because it is always important to remember that the first preview is Friday evening.
There are multiple concerns in a musical: can you dance safely on the floor? is it too slippery? too tacky? can we hear the orchestra? can we hear ourselves? Can we see backstage? Can we make that quick change? Can we get to the other side of the stage in time to make our entrance? Will this hairstyle withstand The Ballet? Can I breathe and sing and dance properly in this corset? Where should I exit? Who is the best person to set the table in this scene? Do the costumes look right in this lighting state? How will we handle this scene change?
The theatre is a tremendously complicated thing, but it is a series of delectable and sometimes maddening problems to solve, all in the name of art. It is always fascinating to think about what has gone in to creating the finished product on the stage.
"The drama is not dead but liveth, and contains the germs of better things."
William Archer, About the Theatre