I think about historical plausibility a lot. Historical costumers worry about accuracy, but I think that ‘accurate’ often gets confused with ‘common’. Just because most seamstresses did something one way, doesn’t necessarily mean that one or two might not have done it completely differently.
Lots of things happen today that aren’t mainstream. Even with the plethora of information on the internet today, people sew, and create, and live in ways that aren’t documented. It is reasonable to assume that historically, there were also seamstresses who created in unusual ways, and used unusual materials.
The costumer who asked me about 18th century masquerade outfits also asked about ideas for making her dress on a limited budget.
I’ve been turning the question over in my mind, and last night (well, 4am in the morning) I had an epiphany. Why not use muslin/calico?
Raw, unpatterned cotton calico (which American’s call muslin) existed in late 18th century Europe. In fact, huge amounts of it were imported, because many countries had passed laws making it illegal to import patterned calico from India in order to protect their own textile industries.
Most 18th century masquerade dresses were just formal dresses, trimmed to represent the idea, allegory, or personage the reveler wanted to dress as. But some people did have specific masquerade outfits made.
Based on extent examples, most formal 18th century frocks were silk. But, that doesn’t mean that the occasional partygoer didn’t use the excuse of the informality of the masquerade as an opportunity to wear a cotton frock.

Robert Dighton, Return from a Masquerade, 1784
I’m sure that the chemise a la reine of the sleepy partygoer above was made of cotton!
I also know of one late 18th century beauty who was the belle of the ball at an international soiree in Germany in a dress of a most unusual material (basically paper) which she described as being styled in the mode of a shepherdess.*
So, with all this in mind, I think it is entirely plausible that there could have been 18th century masquerade dresses made of unpatterned Indian calico. And I think that a costumer on a budget who finds the idea appealing shouldn’t hesitate to make one!
And finally, just some more 18th century masquerade scenes that I have found:

A Chinese themes masquerade in Venice - looks like anything goes when you are dressing up!

Rosalba Carriera. Gustavus Hamilton (1710—1746), Second Viscount Boyne, in Masquerade Costume, 1731-32
Luxurious masquerade costume for an early 18th century gentleman. Don’t you love his lace veil?

Lady Betty Bustle and her maid Lucy prepare for the masquerade
The moon and stars in her hair indicate she may be Diana. I can’t figure out the thing on her skirt.

Dressing for the Masquerade, 1794
A not so flattering depiction of masquerade-goers.

Copy after Jean Antoine Watteau (French, 18th century), The Country Dance
It’s not clear if this painting is meant to represent a real country dance, or masquerade revelers dressed as charmingly bucolic country folk.

The Cascade. Copy after Jean Antoine Watteau (French, 18th century)
Another slightly ambiguous Watteau inspired scene. Are they masqueraders or not?

A Masked Ball in Bohemia. Attributed to Andreas Altomonte (Austrian, 1699—1780), ca 1748




Very traditional Carnivale inspired costumes, along with a smattering of Ottomans and shepherdesses, are the order of the day in this depiction of a mid-century ball in Bohemia. Click on the image to be taken to the Met’s site, where you can see more of it detail.

The Ridotto, Francesco Guardi, ca. 1765
The vignettes in this scene of the famous Venetian Ridotto gambling house and masquerade venue are just adorable:

Isn't the little spinner just too precious? And the girl with the basket: so sweet!

I love the trimming on this dress. The mask is a bit alarming though!

This one is definitely my favourite. I'm such a sucker for pink.

She looks like she is having too good of a time
*I’m planning a project based on the incident, so I don’t want to share too much of my scholarship around it yet.