Cyc, scrim or filled scrim

Rose Brand lists heavyweight muslin in three flame-retardancy classes, and the maximum seamless width differs in each. The non-flame-retardant heavyweight runs to 40'-0" extra wide. The flame-retardant heavyweight runs to 39'-8". The inherently flame-retardant heavyweight stops at 32'-9".

Wide goods hang on their side, so that published width becomes the height of the drop. The certificate a hall accepts therefore fixes the tallest unseamed picture available, before anyone draws one.

Between treated and inherent the gap is close to seven feet. A hall that takes a flame-retardant treatment certificate allows a drop most of a storey taller than a hall that requires inherently flame-retardant goods, from the same supplier and the same weight of cloth.

Nothing about the picture has been decided at that point. The drawing has simply been handed a ceiling by the fire marshal, by way of a weaving loom.

The scrim table lists Sharkstooth Scrim, FR at 39' extra wide, then 35', 31', 24', 19'-6", 15'-6" and 10'-9". The inherently flame-retardant entry above it is a Trevira scrim at 35' extra wide, described on the same page as the same weave as Sharkstooth.

Same weave, same supplier, four feet less seamless width for the inherent certificate. The pattern on the muslin table repeats here at a smaller scale.

One line in that column behaves differently. The 35'-6" entry is listed as Point/3 Thread and carries the comment “More durable, more paint surface.” It gives up some of the openness a bleed-through depends on and returns handling life and a surface that takes scenic paint.

For a concert back wall that matters twice over, because a scrim is usually flown as the tallest soft element on the rig and sits behind everything else that has to clear it.

The same chart lists Leno-filled Scrim, FR at 38'-6", 29'-0" and 19'-0" extra wide, with the comment “weave openings filled-in”.

An open scrim vanishes when the light moves behind it, and that is what a reveal is built on. Filling the weave removes the effect and leaves a wide, paintable surface close to opaque.

So around 38 feet the chart offers both: 39' of Sharkstooth that bleeds through, and 38'-6" of Leno-filled that holds. Two entries six inches apart in width, doing opposite things on a lighting cue. A drawing that says only “scrim” at that height has not yet chosen between them.

The comment column is doing real work here. It is the only place on the chart where the difference between a reveal and a painted surface is written down.

Rose Brand lists its 39' Sharkstooth FR in white and black. The 31' entry adds light grey, light blue and dark blue. The 19'-6" and 15'-6" entries add light blue.

The muslin table behaves the same way. The 40'-0" non-flame-retardant heavyweight is listed in natural. The 39'-8" flame-retardant heavyweight lists black, dark grey, light grey and natural. The 32'-9" inherently flame-retardant heavyweight is listed in white.

Read the two columns together and a tall seamless black drop for a hall that requires inherently flame-retardant goods has no entry on that chart at all. The colour question and the fire question arrive on the same line.

It also runs the other way for a white cyc. The inherently flame-retardant heavyweight is listed in white, so the hall with the strictest certificate is the one best served if the design wanted white to begin with.

The order the tables suggest: ask the venue which certificate it accepts, read the maximum seamless width in that class, and treat that figure as the tallest unseamed drop on offer.

For heavyweight muslin those ceilings are 40'-0" untreated, 39'-8" treated and 32'-9" inherent. For scrim they are 39' treated and 35' inherent.

Above them a drop is still buildable with a horizontal seam, which lands across the picture at whatever height the goods ran out and has to be lit around for the rest of the show.

A trim height past those figures means a seam, a different cloth, or a different back wall altogether, which is the point where an LED wall or a projection surface enters the drawing.

None of those ceilings move with budget or lead time. They are the widths the cloth is woven at, and a drawing that clears them is a drawing that can be built in one piece.