New to gobos, Burned good or bad?

[CSCTech]

Hi guys, we have just started using Gobos in our FOH spots, we have Colortran 5/50s and so we got a theatre mask gobo and a holder and put it in, after focusing worked pretty good, for some reason due to heating and cooling it slid up but that may of been that I did not put it in right or something. Anyways, we used it last night for a show, and when I went to fix it since it slide of, or down for that matter, I noticed that it was black, or burned. I know gobos get red hot in conventional lights due to the heat but are they supposed to turn black? Or should we be using stronger kinds? The one we have is a little flimsy.

 

[Wood4321]

Nope,
after a while they will burn, warp, and eventually burn through.
Just the nature of the medium.
Especially in those old fixtures.
You will get much better gobo life in a source 4, or Selecon pacific.
As far as I have seen, most brands last around the same amount of time.
With apollo lasting a small amount longer than the rest.
Of course YMMV,
Good Luck,
Joshua Wood

 

[Corbettlight]

It seems to me as though any metal heating to "red hot" temperatures would experience oxidation that would blacken it, at least to some degree. I think it's when you get to the point where they're crumbing is when it's time to replace them

 

[MarshallPope]

How black was it? Did it look charred, or was it just darkish? After a while, all gobos will show signs of the heat, but shouldn't actually burn. Where did the gobo come from? I'm assuming it was metal. If so, it should be alright.

EDIT: Ok, apparently I type too slowly. There were no replies yet when I started. ha.

 

[MNicolai]

Something that may contribute to the problem is if you have touched the gobos with your bare hands. Just as with lamps, when the oil from your skin gets heated up on the surfaces, bad things happen and the steel gobos will overheat reach the end of their lives much sooner than normal. It's good practice after handling gobos with bare hands to wipe them off with isopropyl alcohol.

 

[Wood4321]

Ok,
I have seen finger prints burned into gobos,
But I would hesitate to say that it caused the gobo to fail faster.
I have installed thousands of patterns over the years, in moving lights as well as conventionals.
But I have never seen a pattern fail prematurely due to a finger print.

I also wonder if alcohol will cause the patterns to rust faster as well, due to the water content in alcohol, as well as stripping any protective oil on the steel.

Of course, I always use Apollo patterns, (usually customs) but occasionally stock stuff.
And now that I am moving my stock to V*L, I find myself buying less and less metal patterns by the day....

Of course, if a manufacturer come on here and tells me not to touch patterns with my bare hands, i will change my ways.


Joshua Wood

 

[Les]

After a while, all gobos will show signs of the heat, but shouldn't actually burn.

Oh but they do! Even in a Source Four, a gobo will eventually burn out/through. Especially if you have a poorly bench focused fixture. Now in an aluminum reflector fixture such as a 5/50 or 360Q, the time it takes for a burnout will be much shorter. You would probably be good to get a full run out of a frequently used gobo in one of these types of fixtures. This of course varies depending on the density of the pattern (how much steel is in the optical path), lamp type used, overall condition of the fixture, gobo handling practices, etc. (Woodj32177 , believe me, any 'protective oil' that might be on a gobo would burn off immediately, so no need to worry about that If you do notice oil on a gobo, it is most likely a remnant of the manufacturing process and should be removed immediately).

I think what you describe is pretty normal. But you might want to check your bench focus since we don't actually know how bad the gobo looks. You might could make it 'still bad, but less bad'. Good luck!

 

[derekleffew]

From KnowledgeBase: Source Four Heat Ratings/ How Much Heat Does the Source 4 Emit? - Electronic Theatre Controls :

What is the Gate Temperature of a Source Four ERS?
In a test condition created by placing one shutter blade into gate covering 1/2 of field, and placing the thermal probe on the backside (shaded) of the shutter, the maximum S4 gate temps (A-size) were recorded as follows:
HPL 575w/115v/300hr = 622°F
HPL 750w/115v/300hr = 786°F

Remember that a non-dichroic reflector, such as in the Colortran 5/50 or Altman 360Q, will reflect even more infra red energy forward into the gate. Heat any metal to 800°F or more and it will darken significantly. A possible benefit to this phenomenon is that the projected image may appear sharper, due to less unwanted reflections within the optical path.

In the olden days we used to push in each shutter until it was just visible within the field of the gobo, so as to somewhat protect the template from the heat. Not sure it made any real difference in the life of the pattern, however.

From Apollo Design | Steel Gobos :

Apollo metal gobos are made from an 8 mil stainless steel with a high quantity of nickel and chromium that provide longer life and image quality. The majority of alternative products on the market are made from a 5 mil stainless steel comprised of a large amount of carbon steel that begins to oxidize (rust) and breakdown in a shorter period of time. If a magnet sticks to the pattern, it is mainly carbon steel - which means it is not an Apollo pattern.

Fact or marketing hyperbole?

... Of course, if a manufacturer come on here and tells me not to touch patterns with my bare hands, i will change my ways. ...

From VL3000 Luminaire User Manual.pdf, page 58:

CAUTION: Do not touch gobos with bare fingers. Wear cotton gloves or other covering while
replacing. Clean with glass cleaner and soft cloth if required.

 

[CSCTech]

Oh, Alrighty good to know : )

It is a metal Rosco gobo by the way, sorry for not specifying.
I was unaware that touching them wasn't good, I did handle it a bit with my hands. I suppose its just because we have Colortran 5/50s

Thank you!

 

[Les]

Oh, Alrighty good to know : )

It is a metal Rosco gobo by the way, sorry for not specifying.
I was unaware that touching them wasn't good, I did handle it a bit with my hands. I suppose its just because we have Colortran 5/50s

Thank you!

As someone who has handled quite a few gobos with my bare hands with little-to-no adverse effects observed, I think I would agree that though it may be 'frowned upon', your fixture is most likely the culprit in this case. Not saying handling gobos with caution is a bad thing, just most likely not a death sentence for the gobo unless you're just a real dirty person or have been doing a brake job on your car for the past 2 hours.

I still wouldn't make finger fudging a gobo a habit, though.

 

[MarshallPope]

Oh but they do!

I should have clarified further. I took the OP to mean that this was just after a few days/weeks of use, and by that point I wouldn't expect to see serious charred-burnt steel.

 

[Wood4321]

I also would like to clarify,
I was talking about steel patterns, My apologies for not being more clear in my post.
Glass patterns are very much a different beast than steel/Stainless.

Glass should be kept fingerprint free...
And as VL's all require glass patterns only, that is what they are talking about in the VL3000 manual.

Josh

 

[Kelite]

Apollo metal gobos are made from an 8 mil stainless steel with a high quantity of nickel and chromium that provide longer life and image quality. The majority of alternative products on the market are made from a 5 mil stainless steel comprised of a large amount of carbon steel that begins to oxidize (rust) and breakdown in a shorter period of time. If a magnet sticks to the pattern, it is mainly carbon steel - which means it is not an Apollo pattern.

Fact or marketing hyperbole?

Fact.

When Apollo began producing metal gobos via the acid etch process, the alloy was not only inherently harder but much thicker as well. Using .008 inch thick stainless steel (or 8 mils, depending upon the unit of measurement) was a much slower process than acid etching .005 metal commonly used by the other makers. Joel Nichols wanted to produce a better gobo, not just an adequate gobo.

Now that the hazardous waste of chemical etching has been replaced by clean laser technology at Apollo, thousands of gallons of used etchant are NOT being produced as well. That's a good thing.

There was a short time when we tried several different alloys of stainless, some of which were mildly magnetic due to the level of carbon present. While there may be a few of these 'red herring' in the market place, they are rare indeed.



Also- I have seen and used alot of Apollo steel gobos over the years and have yet to see an Apollo steel pattern 'burn through'. Torn, bent, perhaps shredded by incorrect removal, but never 'burned through'. Fingerprints don't adversely affect the steel pattern perfomance or life- just the physical appearance.

 

[GageStryker]

I still have some gobos branded "K-Max" which was lined with the origins of Apollo, (Kelite can probably confirm/deny this). They are significantly thicker patterns, designed to hold up to more punishment, but unfortunately my predecessors didn't have very good taste in gobos so they get rarely used.

I've never seen a pattern, Rosco or Apollo burn completely through in a Source 4. I have seen some older gobos, especially foliage breakups with lots of hanging edges in the pattern become distorted by repeated cooling and heating, but most of those patterns are ten years old or older.

And I've learned the hard way about foliage breakups in twin spin rotators. I've torn the insides out a few times that way. Now I'll use other gobos for my soft focus breakup patterns.

 

[PeteEngel]

Burned gobos are something that most tungsten and HMI units must live with (to one degree or another). at the risk of a blatant product zing, but actually as an example, the following product won't burn gobos.

http://www.robertjuliat.fr/PDF/Documents/Doc_ALEDIN_vGB.pdf

since tungsten units generate a large amount of energy to heat, the metal gobos get to red hot temps fairly quickly. some units use reflectors that draw off some portion of the IR spectrum. (kudos to the temp list for the S4's listed earlier). It might just be something that one must live with in that unit. Th black wouldn't bug me as much as the warping of the metal that will eventually make it hard to focus on all imaging edges at the same time.

 

[Kelite]

I still have some gobos branded "K-Max" which was lined with the origins of Apollo, (Kelite can probably confirm/deny this). They are significantly thicker patterns, designed to hold up to more punishment.

You bet. The original K-Max Apollo gobos designated their long life in 1,000 Watt (1K) fixtures such as the Altman 360Q and Strand / Colortran fixtures. Apollo's patterns, both stock and custom, maintain this thicker stainless steel composition for longer life.

And I've learned the hard way about foliage breakups in twin spin rotators. I've torn the insides out a few times that way. Now I'll use other gobos for my soft focus breakup patterns.

Many of us have found out the hard way about spinning jagged edged gobos in a hot fixture environment, only to get them tangled together. You may continue using your first choice of patterns by placing a clear borosilicate glass disk between the patterns when in a gobo rotator. We offer this item for an MSRP of $15.90 (No sales pitch here- just an effort to solve this often-faced dilemma.)

 

[CSCTech]

Little followup,

The gobo again is a Rosco metal one and it almost feels like aluminum or something sorry not to sure the metal it is, it is rather flimsy.
Anyways, it is used for the opening and intermission of plays. It was used at most 25 minutes on about 60% intensity about 6 times and after that the gobo is a bit warped and you can definitely tell where the lamp is near the gobo, I don't believe it was centerd when put it for some reason, but it was placed in the slot infront of the top shutter and near the middle there is a fairly substantiual burn, however it is not spread over the entire disc, only the middle.

So like you guys have said I will accept it is our 5/50's


One question about gobos,

Why, not sure if this is on all or just Rosco's, but on the bottum of the gobo instead of jsut being round there are teeth. Any reason for it?

Also for some reason, I guessed heating and cooling and warping, even if the gobos was perfectly centered in the holder when put it, the firstt ime it was turned on it was fine, after 5 minutes of use on 60 percent it suddenly tiltedupward slightly out of the cut out, then after being off for about an hour then on for another 10 minutes it went up further then didnt move after that.

Going to have to live with out lights burning them quickly but is there any way to make sure they wont move?
Thanks!

 

[Kelite]

Little followup,

The gobo again is a Rosco metal one and it almost feels like aluminum or something sorry not to sure the metal it is, it is rather flimsy.

Chances are very high the gobo is only 5 mils and the alloy is a bit soft, allowing for more pronounced warpage.

Why, not sure if this is on all or just Rosco's, but on the bottum of the gobo instead of jsut being round there are teeth. Any reason for it?

The notches were added by several manufacturers years ago to assist the gobo in staying in one position when inserted within the lighting instrument. When placed within a channel style holder, which was more common than it is today, the notches prevented the gobo from rotating quite as easily.

 

[CSCTech]

Alrighty, thank you.
I'll try a few things to try and keep the holder more tight around the gobo.

 

[Les]

As long as it's ok with the gobo's owners, you could try bending the edges of the gobo slightly to create a tighter fit.