Invention completed in 1966 by chemist-luthier Hans Olof Hansson, in collaboration with violinist Bronislaw Eichenholz who resaddled to advocate the instrument. Originating in classical use, nowadays mainly in folk music.

In appearance roughly a viola-sized fretless gamba-formed fiddle with 5 strings (c, g, d', a', e"), bowed with viola bow. For schematics, see Proprius 25 04 02 - 009 CA.
Modern invention – not reconstruction – expressly aimed at optimizing volume of resonance, satisfying extended playing techniques (especially on the hitherto too-weak violin part), and timbre equalization over the instrument’s entire register (wherefore only overspun gut strings are used): an instrument built from contemporary scientific findings, coping with earlier literature while, with a minimum of altered technique for its performer, meeting modern needs in acoustics (~volume), extended playing technique (for which the normie violin lacks in resonance & sustain), and sheer pecuniary cutdown (with the physical-chemical analysis (chromatography, IR spectrophotometry) of old primer & varnish amalgamated making the ~“Cremona extra” acoustics available to musicians otherwise unable to obtain such rare instruments. (Hansson, HO: Constructional Principles for Bow Instruments Applied to Violino Grande, the Five‐Stringed New Member of the Violin Family 1969.7.1, The Catgut Acoustical Society Newsletter #11 1969.5.1 p6, Nordwall 1966.8.12 En ny violin med 5 strängar (Expressen)))

Hansson as well as other Swedes were well aware of the then emerging New Violin Family (Hansson also met with Hutchins, but the two had fundamentally different instrumental aims), and ultimately built an own family (among whose members were two 5-string celli (high & low, respectively: a “violoncello grande alto” (C–G–d–a–e') and a “violoncello grande profondo” (F1–C–G–d–a)) developed in collaboration with Siegfried Palm) which has not sustained itself as the violino grande. (Nordwall: The Violino Grande; in Perspectives of New Music 1969, Fall-Winter, pp. 111—114 https://www.jstor.org/stable/832297 p211)

Penderecki’s work nowadays known as Cello Concerto no. 1 was originally written for violino grande (withdrawn to promote the then newly arranged cello piece for Siegfried Palm); cf below and, for details, https://musicbrainz.org/edit/136798502 .

Principal measurements:
Overall length 720 mm
Body length 430 mm
Upper bout 208 mm
Centre bout 137 mm
Lower bout 265 mm
String length 375 mm (on earlier instruments; later around 370 mm according to Hanssons son here)
Rib height 41—44 mm
Sound hole length 96 mmm
(Proprius 25 04 02 - 009 CA)

NOT identical to / to be sorted under https://tickets.metabrainz.org/browse/INST-2 5-string viola since it it has more of a viol-shaped body with sloping shoulders, larger resonating volume of body, in appearance a fretless gamba with a 5 string ambitus of viola & violin combined, tables & ribs meeting at the edge (i.e. not overlapping (as on Hansson’s 1963 prototype here @6:36; and earlier viola-based prototype by Otto Sand collapsed)), played with ordinary viola bow, timbre most cello-ish but with violin clarity and remarkably so consistent throughout its entire ambit of viola + violin combined, and a pizzicato reminiscent in sustain & timbre of guitar.

Its closest kin (not really, as without historical relation) would be the much earlier devised & -funct quinton https://tickets.metabrainz.org/browse/INST-1 ; but the violino grande was created from earlier form only in afterwards correlation to the aim of having common instrumentalists (violasts, violinists (and, for the extended family Hansson later built, cellists)) meet with a minimum of required altered playing technique. Eichenholz repeatedly stated that the violino grande was more easily played than other comparable instruments, and gave up his own violin soloist career at its peak to advocate the new instrument.

N.b. https://tickets.metabrainz.org/browse/INST-2 5-string viola: “Appears on: Played by Mikael Marin on I lust och glöd”; that at https://sv.wikipedia.org/wiki/Mikael_Marin below picture (which clearly shows violin/viola shoulders and cut C-bout ends), he is listed as playing “femsträngad viola, elektrisk viola, violino grande” (= 5-string viola ≠ electric viola ≠ violino grande), also the difference is duly noted on releases:
https://www.discogs.com/release/2561868-Maria-Jonsson-4-Ian-Carr-2-Mikael-Marin-Timber/image/SW1hZ2U6MTI4NjMwNzg4
https://www.discogs.com/master/3482338-Mikael-Marin-Och-Mia-Gustafsson-Mot-Hags%C3%A4tra/image/SW1hZ2U6OTE0NDA2Njg=
https://miamarine.se/index.php/en/band2/marin-marin

RELEASE:
New Swedish Instruments – Proprius 25 04 02 - 009 (1971)

WORKS: SOLO
Karkoff, Maurice: Scitatio, op. 80 (1966; publ. Swedish Music Information Center)
Pergament, Moses: Chaconne ‘Hommage à Bach’ (1941; arr. –64; publ. Swedish Music Information Center)

WORKS: ENSEMBLE
Karkoff, Maurice: Landschaft aus Schreien, op. 86 (1967)
Lutosławski, Witold, arr. Eichenholz: Recitativo e arioso
Penderecki, Krszysztof: 3 Miniatures (= 1967 arr. of earlier vln,pf version [Nordwall p112(,114): “[…] an effect which Penderecki, incidentally, had to discard in the original version of his ‘Three Miniatures’ for violin and piano, later rewritten for violino grande.”]

WORKS: CONCERTANTE WITH ORCHESTRA
> Drew, James Mulcro: 2 concerti (no. 1 (1969) (KLEF 1970 January p43), no. 2 (1993))
> Glaser, Werner Wolf: Konsert (1964; publ. Swedish Music Information Center)
> Lundquist, Torbjörn Iwan: Fervor (1967; publ. Edition Suecia)
> Penderecki, Krzysztof: Concerto for Violino Grande and Orchestra (1966—7) (1st performed without cadenza (unfinished at concert deadline)), rev. → Concerto for Violino Grande and Orchestra (1968); withdrawn (and later reworked as Cello Concerto 1 (1972)
> Pergament, Moses: Concerto per E-viola / Violino grande ed orchestra (1964—5) (N.b. ‘E-viola’ is not another instrument but the composer’s own alias for the violino grande (dubiously omitted in printed source Swedish String Music. A selective catalogue. Svensk Musik / Swedish Music Information Center 1990); cf: “Efter denna odiskutabla framgång kontaktade Eichenholz Pergament för tredje gången. Vid deras möte den 24 mars 1964 hade med sig ett helt nytt instrument, som instrumentmakaren Hans Olof Hansson hade konstruerat. Det var vad han kallade en violino grande (som Pergament tyckte borde heta E-viola). Det speciella med detta instrument var att omfånget utökats en kvint nedåt medelst en femte sträng, en C-sträng. Pergament blev intresserad och ägnade hela sommaren åt att arbeta om sin mer än tjugoåriga Chaconne för E-viola[…]” (Åhlén: Moses Pergament (Gidlund 2016) p215))

TIMELINE:
1961 Sand experimenting at the urge of Eichenholz. Starting point in existing instrumentarium (viola).
1962.8.15 † Sand; Eichenholz then approaches Sand’s pupil Hansson who sets a completely new starting point: to keep existing player technique (thereby also existing literature) for whatever goal reached from physical-acoustical-chemical approach, letting that compromise decide the result instrument’s form.
1963 Hansson prototype with tables overlapping ribs
1966.9.15 1st public demonstration & performance: ISCM at Musikhistoriska Museet, Stockholm, Sweden [Nutida Musik 1966 ISCM issue p9; SvD 1966.9.16 (urklipp i Sohlman vid ‘violininstrument; Övriga’)
1968.8.3 1st international (though ISCM is certainly international) public demonstration & performance: Spaulding Auditorium, New Hampshire, USA https://robertwilloughby.com/archive/1968DartmouthBrochure.pdf p4, 8

LITERATURE:
> Nordwall, Ove: The Violino Grande; in Perspectives of New Music 1969, Fall–Winter, pp. 111–114 https://bibliomusicasapienza.wordpress.com/perspectives-of-new-music/ / https://www.jstor.org/stable/832297
> Sohlman V:828—9; art. violininstrument; Övriga violininstrument: “5-strängat v[iolininstrument] konstruerat 1966 av svensken H[ans] O[lof] Hansson på uppdrag av B Eichenholz; stämning c g d1 a1 e2. Instr:s storlek är som altviolinens men proportionerna är helt avvikande (bl a har det sluttande skuldror). V. förenar violinens och altviolinens tonomfång och klangen påminner om en cello men äger violinens klarhet.”
> Swedish String Music. A selective catalogue. (Svensk Musik / Swedish Music Information Center, Stockholm 1990. ISBN 91-85470-56-2)
> Hansson, HO: Constructional Principles for Bow Instruments Applied to Violino Grande, the Five‐Stringed New Member of the Violin Family 1969.7.1
> The Catgut Acoustical Society Newsletter #11 1969.5.1 p5—6
> Nordwall 1966.8.12 En ny violin med 5 strängar (Expressen)
> History of Viola (p237, PDF p265) has a short mention of the violino grande, nothing new and some errors.

PICTURES:
> Photos: https://auctionet.com/sv/2071691-violino-grande-5-strangat-strakinstrument-c-g-d1-a1-e2
> Schematics: Proprius 25 04 02 - 009