Yes, it's time for another PSA for film-makers.
This has actually been a problem for quite a few people I know who either work in F/X makeup or practical effects, and I'd like to address it since I'm sure we're all getting tired of being kicked in the teeth over things we had no control over.
If you want complicated makeups and practical effects in your film, you have to both give adequate time in pre-production and allow the proper time for them in your shooting schedule. If you absolutely must skip a few highly-recommended steps, such as having life-casts done on actors who need heavy prosthetic creature makeup or meeting with the effects team to go over storyboards and execution plans before shooting, then you cannot expect everything to look exactly the way you've envisioned it.
And if you decide to add or entirely change something on the spot during shooting, you cannot expect your MUA or SPFX team to have anticipated it and have everything they need on hand to instantly accommodate your whim.
I understand that most people have no idea what we go through in order to work our magic. Most directors haven't spent much time in an effects workshop and don't understand that something as “simple” as a weapon prop or a prosthetic makeup piece can take days to build properly. It often amazes people to learn that it can take several hours to shoot an effect that is seen for less than a few seconds on the screen.
In the past year my team has pulled off some miracles that many folks I know in our field would have told the director to go to Hell if those demands were made of them. I'm always completely honest with directors when it comes to expectations, especially if given less than even remotely ideal conditions and circumstances in which to work under. More often than not, we end up making do with whatever we have when even more complications are heaped onto us on location. But I will not tolerate anyone telling me that members of my team suck when I know that they are busting their asses to work for someone with impossible expectations.
If you tell me that you want prosthetic makeup ready to shoot by 10am, then we'll have it camera-ready by 10am. If we have an actor in heavy prosthetics or gelatin blood ready at 10am and you don't call for them until 12pm, chances are very good that the makeup has been pulled out of shape and the blood has crusted over while they were sitting around chatting in the green room. If you don't call for them until after 4pm, chances are even better that they'll need a complete overhaul. If you don't call for them until after 8pm, you'll be lucky if they haven't taken the makeup completely off and gone home. (And if they haven't done that, you'll wish they had because you won't get a good performance out of an extremely pissed-off actor.)
If you tell me that you want a complicated creature but don't have time or money to have us do a life-cast on the actor to make a prosthetic (let alone do a screen test for the makeup) during pre-production, you cannot expect the creature to look exactly that way you want, nor can I tell you exactly what it will look like. Out-of-kit makeups done on the day of shoot depend entirely on the creativity and talent of the MUA to be able to turn someone they've never met before into something that resembles the concept sketch.
As far as in-cam effects go, all the pre-production time in the world is not going to save an effect if it's not given adequate time for execution on set. Few things piss me off more than to have spent a lot of time working on props and gags for an elaborate effect only to end up having to just splash blood around when given no time at all to set up and execute it on shooting day. This is often the result of poor time management on set and scheduling the complicated effects last. My advice to everyone is to get a good UPM on your crew, or at the very least an AD who can crack a whip if you absolutely must shoot long dialog scenes before in-cam effects on the same day. I have never been able to understand why a horror production will spend 90% of its day shooting a dialog scene and then rush through its elaborate effects.
I don't care how experienced your F/X artist is, things can and will go wrong when it comes to in-cam effects and you have to plan for that. I always tell people to expect to need at least two or more takes when it comes to splatter effects because blood is notorious for not taking direction. I also emphasis that effects do take time to set up, and I really prefer being able to meet with directors prior to a shoot in order to show them how gags work and schedule accordingly.
Personally, I always have at least three ways to execute an effect in the event that my best plan goes awry. (Recently I had a gag go south on me on set and had to switch to a couple bleeder tubes I'd built into it for backup because I didn't have enough time to disassemble and fix the spurting mechanism.) But what I am never prepared for are drastic last-minute changes. If you tell me that someone is to die by getting a railroad spike in his face, I am not going to be even remotely prepared to accommodate you if I arrive on set and you tell me that now you want him to be disemboweled with a chainsaw.
Many gags rely on being able to hide mechanisms and components into the surroundings. Changing those surroundings will often compromise the effects set-ups, and it does take some time to figure out how to work around it. If the script calls for a guy to have his leg hacked off in the woods and you decide to change the location to a parking lot, it does mean that the entire effect has to be re-worked. We can't very well just grab a jackhammer and bury some bloke's leg in a hole in the asphalt to achieve the illusion. (And believe me, we cannot build a false floor and dress it to mimic that asphalt in under 5 hours, let alone 5 minutes.)
The same goes with planned shots. If you tell me that a creature will only be shot in mid-range, then the makeup will not be highly detailed for an extreme close-up (It may even be just a mask, as in the case with “background zombies”). If you tell me that an effect will be shot from 10 feet away, then the gag won't be built to show all the kinky little details. (And in the case of effects, it's not uncommon for more than one gag to be needed in order to show both closeups and distance views.)
So please, if you're planning a horror project that requires elaborate makeup and complicted special effects, get your makeup and effects people on board as early as possible and spend a lot of quality time with them. Understand that they can only prepare for what you tell them that you are going to do. Be prepared to compromise if you lack the money or time to do things in the most ideal way, and remember that they can only do the best they can with whatever limits you put on them.