Conventional Fixtures Gel Melting

[photoatdv]

Alright... I really don't have a lot of time to fool around with this, and show's tomorrow.

We replaced some faded blue gels (they'd been up and used for at least a couple of weeks with no drastic bad effects) with another blue gel (similar color, not the same) today and the new gels melted in like 30 seconds. Here's the facts:

-Similar color blue gels
-Melted in ~30 seconds (could be anywhere between 10 seconds and 3 minutes, I wasn't timing)
~ Heat shield between gel and lamp (yes, it was between the gel and lamp... we checked)
- Gel melted but head shield looks fine (not fused together)
~Lights were not refocused/relamped/benched/anything between the gel changes
- Holes are ~2 inches in maybe 20 minutes of use

 

[Sony]

was the old gel HT (High Temperature) type gel? and the new gel not HT? It's obvious with some gel because HT is much thicker than non-HT gel.

 

[photoatdv]

Nope, I have an old piece sitting here as well... the new gel is thicker. Old is rosco 74 I think. Can't remember on the new. Both are very close to the same color.

 

[CSCTech]

Not much to do, I would run out to your supplier and pick up the same, rosco 74, if they have it. If not, try running the fixture lower.

:/ Sorry to hear about your melting.

Heh, I thought large gel sheets I put on our cycs would melt instantly but surprisingly they didnt. (except the tape I used ruined them so they had to be scraped..[Was gaffing tape, Heh, things sure do stick well when heated up!])

 

[xander]

Sometimes a gel batch is just bad. You can try testing more pieces of gel from the same sheet to see if you get the same result and write down the fixture, lamp, gel, time it takes to melt so you can report it. Contact your supplier to try and get your money back/free replacement. Getting more gel sounds like pretty much your only option.

-Tim

 

[derekleffew]

...
- Gel melted but head shield looks fine (not fused together)

What brand and # was the heat shield?

From Apollo Design | Gel Shield - 10" x 10" :

Allow air space between Apollo Gel Shield and color filter in order for hot air to escape.

From Rosco's Super Heat Shield™ :

Super Heat Shield should be positioned between the lens and the color filter, allowing space on each side of the filter for the escape of heated air. Extenders which allow at least 1/2" of air space on each side of the Super Heat Shield will permit adequate venting and insure the longevity of the Super Heat Shield filter.

Many people put the heat shield and color in the same frame, then complain when the color still fades/burns/goes Bonanza.

I agree with the above--if you were using Roscolux 74, and that worked for you, why change? It's very likely that R74, and similarly-colored Roscolux 85, Lee 085, and Lee HT085 all have different tolerances to heat.
Also, a $2 investment in the parts to build your own color extender (double gel frame) will pay off big time in labor and gel savings. In 1984 I was taping cuts of Gelatran to the fronts of top hats. Worked then, still works now.

See also Google search results on CB for burning gel. Lots of threads on the same topic.

 

[photoatdv]

We changed it because the new one was what we had enough of to gel all the lights ... and the old was starting to fade.

 

[JD]

the new gel is thicker.

Wasn't old stock, like Roscolene? Most high temp gels are very thin. Odd to actually have a hole melt on it. What type of fixture? Also, as said above, the heat shield itself can get very hot, so an air gap is required.

 

[WooferHound]

I would want to know the Fixture type, Approximate focal length (degrees angle) of the fixture, and the wattage of the lamp, and even the brand name of the fixture?

sounds like a 1000watt Par 64 VNSP to me . . .

 

[DuckJordan]

What it sounds like is, someone might not actually be using gel but consumer grade light color sheets for house hold lights. If it melted in less than 3 mins then its obviously not correct unless your using a very high end flame thrower on the thing or its a bad gel batch (which do happen).

The information we need on this to help you better is

Fixture Brand:
Fixture Type:
FIxture lamp(wattage):
Fixture Focal degree:

Gel Brand:
Gel Number:

Without that info we can only assume which does absolutely nothing for most problems.

 

[shiben]

If it melted in less than 3 mins then its obviously not correct unless your using a very high end flame thrower on the thing or its a bad gel batch (which do happen).

Hate to quibble on this, but even a low grade flame thrower (scuba tank attached to a gas canister and some sort of igniter in front of the nozzle) will easily melt that gel. Heck, never tried it but I would assume that a can of bug spray and a zippo could do that to gel.

 

[Les]

Hate to quibble on this, but even a low grade flame thrower (scuba tank attached to a gas canister and some sort of igniter in front of the nozzle) will easily melt that gel. Heck, never tried it but I would assume that a can of bug spray and a zippo could do that to gel.

You're probably right! I don't think gel is as inherently "heat proof" as we all assume -- it's just that it is able to dissipate heat quickly. Lay a gel flat on a fresnel lens while it's on and see what happens when it's exposed to a hot surface that introduces heat at a faster rate than it can release it. (Okay, don't really do that unless you want to be scrubbing some lenses for a while).

A similar trick is to hold a filled up water balloon above a candle flame. You can touch the flame to the bottom of the balloon, and the balloon will remain undamaged. This isn't because the rubber is heat proof (or even resistant), it's because the water allows the balloon to get rid of the heat quickly (somewhat like what the air gap on both sides of a cut of gel does).

Many gels will probably melt over a 100w light bulb. I'll have to try it to make sure.

 

[cprted]

I had a bad batch of R80 a while back. The stuff was going Bonanza within 30 mins each time.

If you are still burning through the gel even with correctly used heat shield, you might try putting two or three dozen pin holes in the gel. It won't effect the colour (at least, not in any noticeable way) but will lengthen the life of the gel.

 

[shiben]

Maybe Apollo will introduce a real gel miser: nitrogen cooled gels that you can slot in front of really powerful lights. Plus, you get free fog effects.

 

[WooferHound]

Source 4 fixtures have slots for 2 gel frames. When I insert a single gel I always use the slot farthest from the lens to allow greater airflow which helps the gel and the fixture stay cooler. If your using a heatshield in a S4 light, it should be in a separate frame in the slot closest to the lens.

 

[zmb]

Maybe Apollo will introduce a real gel miser: nitrogen cooled gels that you can slot in front of really powerful lights. Plus, you get free fog effects.

But remember, we don't want anything to shatter if it is dropped or bumped.

 

[gafftapegreenia]

360Q 4.5" Ellipsoidal will melt holes in medium to dark gels almost instantly.

Again what fixtures are these on? If its a permanent thing, dichroic glass might be a good option.

 

[mstaylor]

We used to ventilate all the time in theatre but nobody does anymore. I have suggested to young guys and they look at me like I have three heads. I have used the point of a utility knife but a pattern cutter works better. It looks like a pizza cut with pins on the wheel.

 

[rsmentele]

I have used the pattern cutter vent method many times and it works farly well. I always try to hit anything that is deeply saturated just incase, because we run shows for 6 weeks, and I dont want to be changing gel out every weekend.

 

[derekleffew]

mstaylor and rsmentele , I've never had success using a pounce wheel. To me, it seemed like it just provided a place for the hole to start. See the wiki for the inconclusive opinion of one "gel expert."