Aga Vitreous Enamel
Thursday 7th February 2008
Many customers are amazed by the enamel finish on the front and top of their Aga appliances and want to know more about how it is created. Below is an in depth guide as to how the final product is made
Production
Vitreous
enamel
is
a
process
of
putting
a
coloured
‘glass
' finish
onto
the
outer
surfaces
of
an
appliance
. The
resulting
surface
is
hard
, scratch
and
stain
resistant
(to
varying
degrees
) and
imparts
a
smooth
easily
cleaned
surface
.
Pastel
and
light
colours
are
somewhat
‘softer
' and
are
therefore
slightly
less
resistant
to
scratches
and
stains
.
Many
years
ago
enamels
used
to
contain
lead
, but
whilst
these
gave
a
good
surface
finish
, they
were
extremely
soft
and
could
even
be
stained
by
hot
water
.
All
enamels
used
by
Aga
are
acid
resistant
, conforming
to
current
British
Standards
and
are
also
governed
by
COSH
H regulations
.
The
process
of
vitreous
enamelling
castings
is
as
follows
.
1
. Machined
castings
are
received
from
our
foundry
.
2
. After
checking
, the
components
go
for
annealing
. This
involves
processing
in
the
furnace
at
a
temperature
approximately
30
degrees
higher
than
that
required
for
enamelling
. Annealing
relieves
casting
stresses
, burns
off
surface
impurities
and
slightly
softens
the
metal
.
3
. Following
annealing
, the
castings
are
shot
-blasted
and
then
inspected
and
any
blemishes
filled
. The
fill
paste
is
a
ceramic
water
based
substance
.
4
. Prior
to
the
mid
-fifties
‘direct
-on
' enamelling
was
used
, but
changes
in
the
actual
casting
metal
constituents
made
for
poor
appearance
and
surface
finish
. A
water
-based
ground
coat
is
therefore
applied
by
hand
spraying
, after
which
a
drying
period
of
around
1
-hour
is
carried
out
in
an
oven
to
remove
the
water
and
prevent
it
attacking
the
metal
underneath
the
enamel
coating
. It
also
prevents
pockets
of
water
turning
to
steam
pressure
during
firing
. The
ground
coat
is
approximately
7
thousands
of
an
inch
thick
and
generally
improves
adherence
and
appearance
.
5
. After
drying
, the
ground
coat
is
fired
to
bake
it
on
, at
a
temperature
of
approximately
800
deg
.C
, depending
on
colour
, for
45
minutes
. It
is
allowed
to
cool
naturally
, following
which
a
check
is
made
of
the
enamel
thickness
.
6
. The
topcoat
is
then
sprayed
on
, normally
two
coats
for
an
Aga
, but
a
third
is
sometimes
applied
. Enamel
is
then
dried
for
about
3
hours
(slightly
longer
for
Red
) then
fired
at
around
770
deg
for
45
minutes
. This
process
is
repeated
for
further
coats
. All
components
are
then
subjected
to
quality
checks
for
colour
etc
. Temperatures
in
the
furnace
are
critical
within
a
few
degrees
, as
is
the
length
of
firing
time
, as
overheating
can
affect
colour
shades
. The
colour
matching
of
doors
to
front
plates
is
generally
done
from
stock
but
some
special
matching
by
temperature
can
be
done
.
The
enamel
process
will
cause
castings
to
‘grow
' by
around
2mm
per
30mm
length
, dependent
on
the
number
of
times
that
it
has
been
fired
.
Click here for more information about how to clean your Aga
Quality
The
finish
of
vitreous
enamel
is
subject
to
the
requirements
of
British
Standards
3831
:1964
, from
which
the
following
extracts
are
taken
.
‘Some
minor
faults
may
be
permitted
if
they
are
not
visible
from
the
normal
inspection
distance
of
3
feet
. On
the
other
hand
, certain
blemishes
, which
are
so
obvious
as
to
spoil
the
appearance
of
the
complete
appliance
from
the
users
point
of
view
, may
, as
indicated
in
the
following
clauses
, constitute
non
-compliance
with
this
standard
.
The
quality
of
the
finish
shall
comply
with
the
following
requirements
:
1
. Cracks
: The
enamel
surface
shall
contain
no
cracks
.
2
. Flaking
: The
enamel
shall
not
have
flaked
off
any
enamelled
surfaces
.
The
quality
of
the
finish
may
show
the
following
imperfections
subject
to
the
conditions
stated
:
(i
) Hair
lines
and
strain
lines
: Hair
lines
or
strain
lines
of
ground
coat
showing
through
the
top
coat
with
no
break
or
crack
in
the
enamel
are
permitted
provided
that
they
do
not
detract
from
the
general
appearance
of
the
appliance
.
(ii
) Tears
(beads
) : Tears
(beads
) are
permitted
provided
that
they
do
not
detract
from
the
appearance
or
function
of
the
appliance
in
service
.
(iii
) Runs
(drain
lines
): Runs
(drain
lines
) are
permitted
provided
that
they
do
not
detract
from
the
appearance
or
function
of
the
appliance
in
service
.
(iv
) Pinholes
: There
shall
be
no
holes
in
the
enamel
surface
, which
can
be
shown
to
extend
to
the
base
metal
. For
pinholes
, which
do
not
penetrate
the
ground
coat
the
requirements
given
in
sub
-clause
, (vii
) below
for
specks
shall
apply
.
(v
) Blisters
: Blisters
are
permitted
provided
that
due
to
the
particular
design
or
fabrication
of
the
article
they
are
unavoidable
, and
do
not
detract
from
the
appearance
or
function
of
the
appliance
in
service
.
(vi
) Depressions
and
raised
areas
: Smooth
, well
covered
depressions
or
raised
areas
in
the
enamel
surface
are
permitted
provided
they
are
small
and
widely
spaced
.
(vii
) Specks
and
inclusions
: Specks
showing
on
or
through
the
enamel
surface
are
permitted
provided
that
they
are
not
concentrated
in
one
area
and
are
not
greater
than
1/32
" in
diameter
and
provided
that
they
do
not
detract
from
the
general
appearance
of
the
appliance
.
(viii
) Orange
Peel
(ripple
) Orange
peel
(ripple
) is
permitted
provided
that
it
does
not
detract
from
the
general
appearance
of
the
appliance
.'
An
‘orange
peel
' finish
, although
perhaps
less
attractive
, is
thinner
and
is
more
hard
wearing
and
scratch
resistant
.
