RHX Experiments at Institut de Physique du Globe de

Paris (IPGP)

Maxime LeGoff and Yves Gallet,

Equipe de Paléomagnétisme

Air lock

Saturated salt

Fan

cooler

Temperatureand humidity

probe

Carousel withten baskets

50 cm

Weighingplateau

Air lock

Saturated salt

Fan

cooler

Temperatureand humidity

probe

Carousel withten baskets

50 cm

Weighingplateau

Our equipment:A balance Mettler XP26 placed in a large wine

cellar. 10 samples can automatically be weighed at a same time thanks to a rotating

carrousel, to which small baskets are hanged.

This device was designed to make possible relative RHX dating on samples having

experienced the same environmental conditions during their lifetime AND during the

weighing experiments.

A furnace with temperature regulated and monitored during heating (in air) duration.

(video follows)

-100

-50

0

50

100

0 24 48 72

Fra

ct.

m v

aria

tio

ns

rela

tive

to

th

e en

din

g 1

5 h

mea

n (

pp

m)

-15

-14

-13

-12

-11

-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

1

2

3

4

5

Time (h)

T (°C)

RH (%)33.8%

13°C

-100

-50

0

50

100

1 1.5 2 2.5 3

time1/4 (h1/4)

time (h)

one of our w

eaker gradient afte

r 105°C

Baseline of our apparatus.

- The variations in RH and T are really weak.

- After about 1 day of “natural” drying inside our large climate chamber, the mass stability

stands within about 10 ppm (after filtering the effect of small RH oscillations, not shown here).

Lots Provenance Type Age (y) Fragts specimens HB09 Hosp. de Beaune brique pavment 560 1 10 Ecouen Ecouen brique pavment 460 2 2 x 5sp Mixte01

Ecouen Langres

brique pavment brique pavment

460 460

2 3

1 + 1 3 + 2 + 3

Mixte02 Bois d'Epense Ancy le Franc

biscuit biscuit

230 230

3 2

3 x 2sp 2 x 2sp

Mixte03 SiO2 Langres Bois d'Epense Ancy le Franc

- biscuit biscuit biscuit

- 460 230 230

- 1 3 3

1 1 3

1 + 1 + 3

Mixte04 Mixte04A

Bois d'Epense Ecouen Hosp. de Beaune

biscuit brique pavment brique pavment

230 460 560

3 1 1

3 x 4sp 1 x 4sp 1 x 4sp

Lezoux01 Lezoux02

Lezoux sam. w. 1800 10 10 x 2sp

Lezoux03 Lezoux SiO2

sam. w. -

1800 -

8 -

8 x 1sp 2

Lezoux04 Lezoux05

LEZ01 sam. w. 1800 5 5 x 4sp

Syrie01 - Syrie02 Lot 40 Lot 41

ceramique ceramique

950 860

3 2

3 x 4sp 2 x 4sp

SJC01 Wilson's team - - 5 5 x 2sp

15 groups of 10 samples of different origins and ages have been analyzed

since January, 2012, leading to 470 temporal series

(with weighing duration between several days and several weeks).

Our measurements

Weighing series after drying at 105°C

Example of 7 series of 10 samples weighed after drying at 105°Cduring several hours (min. 5h) up to 2 weeks

done before stabilization of room air temperature

-0.00005

0.00000

0.00005

0.00010

0.00015

0.00020

0.00025

0.00030

0.00035

0 0.5 1 1.5 2 2.5 3 3.5

time1/4 (h1/4)

frac

tio

nal

mas

s g

ain

, fm

gR

X

-4

-3

-2

-1

0

1

2

3

4

5

6

7

8

9

10

LEZ01-01c LEZ01-01d

LEZ01-02c LEZ01-02d

LEZ01-06c LEZ01-06d

LEZ01-09c LEZ01-09d

LEZ01-18c LEZ01-18d

LEZ01 105°C and Dessiccatorthin lines : 10 samples (a;b) after 246h at 105°C;

thick lines : 5 samples (c) 23h at 105°C and 5 twins (d) 23h in dessiccator

3 -> 81h

ΔT (°C)

ΔRH (%)

13.15°C

34%

same time1/4 rangefor the Linear Regression

50ppm

a b

a b

a b

a b

a b

-0.00005

0.00000

0.00005

0.00010

0.00015

0.00020

0.00025

0.00030

0.00035

0 0.5 1 1.5 2 2.5 3 3.5

time1/4 (h1/4)

frac

tio

nal

mas

s g

ain

, fm

gR

X

-4

-3

-2

-1

0

1

2

3

4

5

6

7

8

9

10

LEZ01-06c LEZ01-06d

LEZ01-18c LEZ01-18d

3 -> 81h

ΔT (°C)

ΔRH (%)

13.15°C

34%

same time1/4 rangefor the Linear Regression

50ppm

LEZ01 105°C and Dessiccatorthin lines : 10 samples (a;b) after 246h at 105°C;

thick lines : 5 samples (c) 23h at 105°C and 5 twins (d) 23h in dessiccator

With 4 specimens (a, b, c, d) studied per fragment, these experiments show that:1) there is no mass gain when the samples are not heated

2) the heating duration (1d or 10d) has only a small influence on the “gradient” after drying

twins c;d

short series

twins a;b

Weighing measurements after dehydroxylation at 500°C

-2000

-1000

0

1000

2000

3000

4000

5000

0 1 2 3 4 5

frac

tio

nal

mas

s g

ain

(p

pm

)

-5-4-3-2-10123456789101112131415161718192021222324252627282930

ΔT

(°C

) ;

ΔR

H (

%)

HB01-09b HB01-09a

EC02-05b EC02-05a

BDE01-05b BDE01-05a

BDE01-04b BDE01-04a

BDE01-01b BDE01-01a

Time (h1/4) 4.7 --> 500 H

T

RH

-500

0

500

1000

1500

2000

2500

3000

3500

4000

0 1 2 3 4 5

frac

tio

nal

mas

s g

ain

(p

pm

)

-4

-3

-2

-1

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

Time1/4 (h1/4)

ΔT

(°C

) ;

ΔR

H (

%)

1er - Ph2 2e - #8

2e - #7 2e - #6

2e - #5 2e - #4

2e - #3 2e - #2

2e - #1 2e - Ph6

ΔT (°C)

ΔRH (%)

-2000

-1000

0

1000

2000

3000

4000

5000

6000

7000

8000

0 1 2 3 4 5

Time 1/4 (h 1/4)

Fra

ctio

nal

mas

s g

ain

(p

pm

)

-2

-1

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

ΔT

(°C

) ;

ΔR

H (

%)

Lot41-05d Lot41-05c

Lot41-01d Lot41-01c

Lot40-08d Lot40-08c

Lot40-07d Lot40-07c

Lot40-06d Lot40-06c

Three examples of 10 long series of rehydroxylation measurements obtained after heating at 500°C.

Twin samples often show different behaviors and normal, concave

and convex behaviors are simultaneously observed.

For the samian ware of Lezoux, with unstable climate conditions (breakdown of our conditioned air system), the related mass variations are practically negligible.

3 sites from France (500°C : 72h)

2 sites from Syria (500°C : 67h)

10 Lezoux (France) (500°C : 117h)

2 Ecouen

2 Hosp. de Beaune

3 x 2 Bois d’Epense

-0.0005

0.0000

0.0005

0.0010

0.0015

0.0020

0.0025

0.0030

0.0035

0.0040

0 1 2 3 4 5

1er - Ph2 2e - #8

2e - #7 2e - #6

2e - #5 2e - #4

2e - #3 2e - #2

2e - #1 2e - Ph6LEZOUX : 1/N = 1/4

On the difficulty to test the 1/4 power law

-0.0005

0.0000

0.0005

0.0010

0.0015

0.0020

0.0025

0.0030

0.0035

0.0040

0 1 2 3 4 5 6 7 8 9 10

1er - Ph2 2e - #8

2e - #7 2e - #6

2e - #5 2e - #4

2e - #3 2e - #2

2e - #1 2e - Ph6

LEZOUX : 1/N = 1/3

Possibility for other exponent...

Deriving RHX dating

730

y

47

y 513

y

259

y2

67 y

460

y

532

y

14

y

907

y

337

y

-10000

0

10000

20000

30000

40000

50000

60000

70000

0 10 20 30 40 50

Lot40-06c Lot40-06d

Lot40-07c Lot40-07d

Lot40-08c Lot40-08d

Lot41-01c Lot41-01d

Lot41-05c Lot41-05d-2000

0

2000

4000

6000

8000

0 1 2 3 4

time (h1/4)

frac

tio

nal

mas

s g

ain

(p

pm

)

Example of calculation for 10 samples from 2 Syrian sites.

The RHX age is calculated by extending the RHX regression line to its intersect with the horizontal line which is the presumed archeological mass (mA).

In this example, all samples share the same time range for the regression calculation. Of course, this is not a general rule and each sample should be individually analyzed.

archeo : 860 / 970 y

Age Pre

sum

é

0

5000

10000

15000

20000

25000

0 10 20 30 40 50 60

These two animated figures show individual age computations using variable timespans (including the end of the series) for the linear

regression calculation.

They concern two samples from Syrian Lot40

One, in the top panel, is clearly convex, whereas the second, in the

bottom panel is "normal".

But both fail to give a realistic age.

This synthetic series, based on realistic parameters with an age of 2000 years, can be analyzed as a short (about 3 h1/4) or as a long (about 5 h1/4) time of weighing.

The top and the left panels show the recalculation of the RHX age by a timespan analysis (see the arrows). This analysis provides important information on the

reliability of the derived RHX dating: the latter is considered as reliable only if a plateau is observed.

(Animated sequence of five different views, each corresponding to a new randomization)

-1000

-500

0

500

1000

1500

2000

1.5 2 2.5 3 3.5 4 4.5Beginning of time1/4 span (h1/4)

Ag

e (y

)

0

100

200

300

400

500

600

700

Ag

e (

y)

EC02-05b EC02-05a HB01-09b HB01-09a BDE01-05b

BDE01-05a BDE01-04b BDE01-04a BDE01-01b BDE01-01a

-600

-400

-200

0

200

400

600

800

1000

1200

2 2.5 3 3.5 4 4.5Time 1/4 (h 1/4)

RH

X A

ge

(y)

0

50

100

150

200

250

300

RH

X A

ge

(y)

Lot40-08d Lot40-08c Lot40-07d Lot41-05d Lot41-05c

Lot40-07c Lot40-06d Lot40-06c Lot41-01d Lot41-01c

Lot 40, Age : 965 ±60 y

Lot 41, Age : 860 ±40 y

Timespan analysis for 10 samples from 3 French sites,

and 10 samples from 2 Syrian sites.

The horizontal dashed lines show the known archeological dates.

More or less convincing plateau ages are only observed for some of

the Syrian samples

CONCLUSIONS

The numerous measurements carried out using the automatic weighing device constructed in our laboratory all fail in reproducing satisfactory RHX dating results,

such as those in Wilson et al. (2009)’s study (we recall that for the latter study neither Energy Activation (Ea) nor Effective

Lifetime Temperature (ELT) corrections were applied).

Our ages are often too young, but in some cases they are much too old. Even if the ELT has a large effect on the RHX gradient, the correction for this effect would

generally be insufficient to obtain good RHX dating results.

The main difficulty is that twin samples (i.e. obtained from the same fragment!) show only rarely the same RHX behavior, and consequently give the same RHX age.

Another difficulty is that each new heating (at low or high temperature) result in a significant loss of mass, as well as if we change by a few degrees the reference

temperatures (105°C and 500°C) :Do these temperatures have physical meaning?